Biological fluid filtration apparatus

ABSTRACT

Biological fluid filtration systems including biological fluid filtration devices capable of filtering blood or blood products, including the removal of leukocytes from the blood or blood product. Each system includes a means to automatically drain the biological fluid upstream of the biological fluid filtration media disposed in the biological fluid filtration device. Both single sided and double sided biological fluid filtration devices are disclosed, including double sided biological fluid filtration devices with a solid partition wall with a first independent fluid flow path on one side of the partition wall, and a second independent fluid flow path on the other side of the partition wall. Draining means include vent filtration devices, diaphragm draining devices, and biological fluid filtration devices that include an integral diaphragm. The biological fluid filtration devices include low hold-up volume filter underdrains that purge in excess of 95% of the initial air in the device before liquid begins to flow from the outlet, thereby allowing the devices to be used in bed side applications. Variable surface area biological fluid filtration devices are disclosed that further reduce hold-up volume.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.10/934,881, filed Sep. 3, 2004, for A Biological Fluid Filter Apparatus.Application Ser. No. 10/934,881, pursuant to 35 U.S.C. §119(e)(1),claimed priority from Provisional Application Ser. No. 60/500,970, filedSep. 5, 2003, and of Provisional Application Ser. No. 60/524,014, filedNov. 20, 2003. Application Ser. No. 10/934,881 is pending as of thefiling date of the present application.

BACKGROUND OF THE INVENTION

This invention relates to the filtration field, and more particularly,to an improved low hold up biological fluid filtration system, includinga low hold up biological fluid filter device capable of filteringbiological fluids, including the removal of components or chemicals fromblood or blood products, and including the removal of leukocytes frompacked red cells, and prions from blood or blood products.

There are currently available filtration devices for filtering blood orblood products. The currently available devices use multiple layers offiltration media of different pore size, but of the same diameter. Somedevices use a vent filter to drain the upstream side of the filtrationdevice after filtration is complete to minimize hold up volume. Thesevent filters either have to be isolated from the fluid being filteredduring the filtration cycle by a clamp or valve which has to be manuallyopened once filtration is complete to drain the device, or in anautomatic system multiple layers of different pore size vent filtermedia must be used to prevent fouling the vent filter during thefiltration cycle. Some of these devices require a negative pressure onthe outlet of the device to eliminate air from the downstream side ofthe device. In all of the devices a quantity of biological fluid willflow from the outlet of the device before all of the air has been purgedfrom the device. For a device to be usable in bed side applications(i.e. for direct transfusion to a patient), the amount of biologicalfluid that flows from the outlet of the device before all of the air hasbeen purged from the device must be minimized. Furthermore, currentlyavailable filtration devices are designed to filter one type of blood orblood product per device.

It is therefore an object of the present invention to provide abiological fluid filtration system including a biological fluidfiltration device that runs automatically, minimizes hold up volume,does not require a negative pressure at the outlet to eliminate air fromthe down stream side of the biological fluid filtration device, and inseveral embodiments use smaller surface area downstream filter elementsto reduce hold up volume of the device. It is also an object of thepresent invention to minimize the amount of biological fluid that flowsfrom the outlet of the biological fluid filtration device before all ofthe air has been purged from the device, so that the biological fluidfiltration device will be usable in bed side applications. It is afurther object of the present invention to eliminate the need for ventfilters to drain the upstream chamber of the biological fluid filtrationdevice after the filtration cycle has been completed. Another object ofthe present invention is to be able to filter two different types ofblood or blood product using a single biological fluid filtration devicethat includes two independent fluid flow paths, without fluid flowcommunication between the two fluid flow paths. For example leukocytescould be removed from packed red cells through one fluid flow path, andleukocytes could be removed from a platelet concentrate through theother fluid flow path. It is also an object of the present invention toprovide a single vent filtration device that can vent the two fluid flowpaths of a biological fluid filtration device that includes twoindependent fluid flow paths.

DEFINITIONS

A Biological Fluid Filtration Device (hereinafter referred to as BFFD)as used herein means a filtration device comprising a housing containingan inlet and an outlet, with a fluid flow path defined between the inletand the outlet, with a biological fluid filtration media interposedbetween the inlet and the outlet and across the fluid flow path, andsealed to the housing to prevent the flow of biological fluid betweenthe housing and the biological fluid filtration media. The biologicalfluid filtration device being capable of filtering biological fluids,including blood or blood products to remove leukocytes, prions, otherblood components, cells, and chemical agents which may be used to treatthe biological fluid, from the biological fluid. A biological fluidfiltration device that contains a single inlet and a single outlet withone biological fluid filtration media interposed between the inlet andthe outlet may be referred to as a single sided biological fluidfiltration device. The term Biological Fluid Filtration Device may alsorefer to a filtration device comprising a housing containing two inletsand two outlets, with a first fluid flow path defined between the firstinlet and the first outlet, with a first biological fluid filtrationmedia interposed between the first inlet and the first outlet and acrossthe first fluid flow path, and sealed to the housing to prevent the flowof biological fluid between the housing and the first biological fluidfiltration media; and with a second independent fluid flow path definedbetween the second inlet and the second outlet, with a second biologicalfluid filtration media interposed between the second inlet and thesecond outlet and across the second fluid flow path, and sealed to thehousing to prevent the flow of biological fluid between the housing andthe second biological fluid filtration media. The biological fluidfiltration device that contains two independent fluid flow paths beingcapable of simultaneously filtering two different types biologicalfluids, including blood or blood products to remove leukocytes, prions,other blood components, cells, and chemical agents which may be used totreat the biological fluid, from the biological fluid. A biologicalfluid filtration device that contains a single inlet and a single outletwith two biological fluid filtration media interposed between the inletand the outlet, with a first fluid flow path flowing from the inlet,through the first biological fluid filtration media to the outlet, andwith a second fluid flow path flowing from the inlet, through the secondbiological fluid filtration media to the outlet, may be referred to as adouble sided biological fluid filtration device. Likewise, a biologicalfluid filtration device that contains two inlets and two outlets, with afirst fluid flow path flowing from the first inlet, through the firstbiological fluid filtration media to the first outlet, and with a secondfluid flow path flowing from the second inlet, through the secondbiological fluid filtration media to the second outlet, may also bereferred to as a double sided biological fluid filtration device.

Biological Fluid Filtration Media (hereinafter referred to as BFFM) asused herein means a porous filtration media capable of filteringbiological fluids, including blood or blood products to removeleukocytes, prions, other blood components, cells, and chemical agentswhich may be used to treat the biological fluid, from the biologicalfluid. The biological fluid filtration media (BFFM) comprises at leastone filter element, with each filter element containing one or morelayers of porous filter material of the same type. The biological fluidfiltration media may contain more than one filter element, with eachfilter element containing a different type of filter material.

Vent Filtration Media as used herein means the filtration media used ina vent filter device. The media may be microporous filter material madefrom a material such as Teflon or PVDF, preferably with a pore size of0.2μ or smaller, or the media may be a depth media, such as cotton, spunbound polyester, or a molded depth media such as Porex.

Housing as used herein means the enclosure into which the filtrationmedia is sealed. The housing of a BFFD contains an inlet and an outlet,with a fluid flow path defined between the inlet and the outlet, with aBFFM interposed between the inlet and the outlet and across the fluidflow path, and sealed to the housing to prevent the flow of biologicalfluid between the housing and the BFFM. The housing of a BFFD maycontain two inlets and two outlets, with a first fluid flow path definedbetween the first inlet and the first outlet, with a first BFFMinterposed between the first inlet and the first outlet and across thefirst fluid flow path, and sealed to the housing to prevent the flow ofbiological fluid between the housing and the first BFFM; and with asecond fluid flow path defined between the second inlet and the secondoutlet, with a second BFFM interposed between the second inlet and thesecond outlet and across the second fluid flow path, and sealed to thehousing to prevent the flow of biological fluid between the housing andthe second BFFM. The housing may be made from a rigid material such asstainless steel or aluminum, or from any rigid molded plastic materialsuch as Acrylic, Polycarbonate, Polypropylene, Polyethylene, or from anyflexible plastic film material such as PVC, Polypropylene, Polyethylene,or from a combination of rigid and flexible materials. The housing of avent filtration device contains a vent port in fluid flow communicationwith atmosphere, and a system port in fluid flow communication with thebiological fluid filtration system, with a fluid flow path definedbetween the vent port and the system port, with a vent filtration mediainterposed between the vent port and the system port and across thefluid flow path, and sealed to the housing to prevent the flow ofbiological fluid or gas between the vent filtration media and thehousing. Alternately the housing of a vent filtration device may containa vent port in fluid flow communication with atmosphere, and a firstsystem port in fluid flow communication with the biological fluidfiltration system, with a first fluid flow path defined between the ventport and the first system port, with a vent filtration media interposedbetween the vent port and the first system port and across the firstfluid flow path, and sealed to the housing to prevent the flow ofbiological fluid or gas between the vent filtration media and thehousing; and a second system port in fluid flow communication with thebiological fluid filtration system, with a second fluid flow pathdefined between the vent port and the second system port, with a ventfiltration media interposed between the vent port and the second systemport and across the second fluid flow path, and sealed to the housing toprevent the flow of biological fluid or gas between the vent filtrationmedia and the housing.

Three Tube Connector as used herein means a tubing connector containingthree tube sockets. One end of a first length of tubing is connected tothe first tube socket, one end of a second length of tubing is connectedto the second tube socket, and one end of a third length of tubing isconnected to the third tube socket. The three tube connector contains acommon node that is in fluid flow communication with the three lengthsof tubing. A tubing Tee is one form of a three tube connector. A tubingY is another form of a three tube connector.

Biological Fluid as used herein means any type of biological liquid,including blood or blood product, and including leukocyte containingsuspensions or a prion containing suspensions.

Leukocyte Containing Suspension as used herein means a liquid in whichleukocytes are suspended. Examples of leukocyte-containing suspensionsinclude whole blood; red cell products, such as concentrated red cells,washed red cells, leukocyte-removed cells, thawed red cell concentrateand thawed red cell suspension; plasma products, such as platelet-poorplasma, platelet-enriched plasma, fresh lyophilized plasma, fresh liquidplasma and cryoprecipitate; and other leukocyte-containing bloodproducts, such as concentrated platelet cells, buffy coat and buffycoat-removed blood. The leukocyte-containing suspension to be filteredby the devices and systems described in the present invention is notlimited to the above examples.

Prion Containing Suspension as used herein means a liquid in whichprions are suspended.

Diaphragm Draining Device (hereinafter referred to as DDD) as usedherein means a device having a housing with an inlet in fluid flowcommunication with atmosphere, with an outlet in fluid flowcommunication with a second device to be drained, and with a diaphragminterposed between the inlet and the outlet, with the housing containinga volume of gas between the diaphragm and the outlet in its normalstate.

SUMMARY OF THE INVENTION

The foregoing problems of the prior art are solved, and the objects ofthe present invention are achieved, by use of a biological fluidfiltration device (BFFD) and system constructed in accordance with theprinciples of the present invention. The biological fluid filtrationsystem of the present invention is capable of filtering biologicalfluids, including blood or blood products to remove leukocytes, prions,other blood components, cells, and chemical agents which may be used totreat the biological fluid, from the biological fluid.

The biological fluid filtration system includes a feed container,normally a collapsible blood bag and a receiving container, normally acollapsible blood bag with a BFFD interposed between the two blood bags.The BFFD includes a housing having an inlet and an outlet with a fluidflow path defined between the inlet and the outlet. A biological fluidfiltration media (BFFM) is interposed between the inlet and the outlet,and across the fluid flow path. The BFFM may contain one filter elementor multiple filter elements of different types. The housing alsoincludes a chamber located between the inlet and the upstream surface ofthe BFFM. In several embodiments the housing also includes an outletchannel interposed between the downstream side of the BFFM and theoutlet, with the outlet channel being in direct fluid flow relation withthe outlet port, and with at least the portion of the outlet channeladjoining the outlet having a cross sectional flow area greater than thecross sectional flow area of the outlet.

In another embodiment of the BFFD an outlet chamber or plenum isinterposed between the downstream side of the BFFM and the outlet.

Several embodiments of the biological fluid filtration system include athree tube connector inserted into the length of tubing between the feedcontainer and the inlet of the BFFD, so that a first length of tubingconnects the feed container to a first port on the three tube connector,and a second length of tubing connects the inlet of the BFFD to a secondport on the three tube connector, and a third length of tubing connectsa vent filtration device to the third port of the three tube connector.The vent filtration device contains a vent port in fluid flowcommunication with atmosphere. The three tube connector contains acommon node. A first flow path is defined between the feed container andthe common node. A second flow path is defined between the common nodeand the inlet of the BFFD. A third flow path is defined between thecommon node and the vent port. The distance between the top of thebiological liquid in the feed container and the common node must begreater than the distance between the common node and the inlet of theBFFD until the BFFM in the BFFD has been wetted with biological liquid.A portion of the second fluid flow path is disposed above the commonnode a sufficient distance to create a positive pressure at the commonnode whenever biological liquid flows through the first and second fluidflow paths, thereby preventing air from entering the system wheneverbiological liquid flows through the first fluid flow path and throughthe second fluid flow path without the need to manually close the thirdfluid flow path. Alternately the three tube connector can contain a flowrestriction in the second flow path in which case a portion of thesecond fluid flow path does not have to be disposed above the commonnode. In either case the vent filtration device could be replaced with adiaphragm draining device defined above, and described below.

Alternately, the BFFD may contain a second inlet upstream of the BFFM. Avent filtration device containing a vent filter element is connected tothe second inlet via a length of tubing. The vent filtration devicecontains a vent port in fluid flow communication with atmosphere, and afluid flow path is defined between the vent port and the upstreamchamber of the BFFD, with the vent filter element interposed between thevent port and the second inlet of the BFFD, and across the fluid flowpath.

Several embodiments of the BFFD include a diaphragm disposed upstream ofthe BFFM. In the normal state of the diaphragm an upstream chamber isdefined between the upstream surface of the BFFM and the inner surfaceof the diaphragm, with the inlet in fluid flow communication with theupstream chamber. When the filtration cycle is complete and the feedblood bag is emptied, the negative pressure created by the column offiltered biological fluid in the outlet tubing causes the diaphragm tocollapse onto the upstream surface of the BFFM, thereby forcing theunfiltered biological fluid in the upstream chamber through the BFFMinto the outlet, thereby minimizing hold up volume.

To further reduce hold up volume several embodiments of the BFFD containvariable surface area filter elements, with one or more filter elementsof a first surface area, followed by one or more filter elements of asecond smaller surface area. Interposed between the larger surface areafilter elements and the smaller surface area filter elements is a flowdistribution filter element with a pore size greater than that of theothers.

Several embodiments of the BFFD contain a single inlet and a singleoutlet with two sets of BFFM, each set having variable surface area.

Several embodiments of the BFFD contain a housing with a solid partitionwall that divides the housing into two independent BFFD's, with twoindependent flow paths. The BFFD is capable of filtering two differenttypes of biological fluid simultaneously. For example, a unit of packedred blood cells can be filtered through the first fluid flow path on oneside of the solid partition wall, while a unit of blood platelets can befiltered through the second fluid flow path on the other side of thesolid partition wall. Each fluid flow path may contain a different typeof BFFM. The BFFM could also be used to filter two independent units ofthe same type of biological fluid.

An embodiment of a biological fluid filtration system that uses a BFFDwith a solid partition wall, also contains a vent filtration device thatcan vent the two BFFD's on either side of the solid partition wallsimultaneously.

In any of the embodiments the BFFM may include a first filter elementcomposed of one or more layers of porous filter material of a first poresize, followed by a second filter element composed of one or more layersof porous filter material of a second pore size smaller than that of thefirst pore size, followed by a third filter element composed of one ormore layers of porous filter material of a third pore size larger thanthat of the second pore size, followed by a fourth filter elementcomposed of one or more layers of porous filter material of a fourthpore size smaller than the pore size of the second filter element. Thefirst filter element may include means to remove gels from blood orblood product, the second filter element may include means to removemicroaggregates from blood or blood products, the fourth filter elementmay include means to remove leukocytes from blood or blood products,while the third filter element acts as a flow distribution layer.

In any of the embodiments a vent filtration device may be added to aport on the receiving container normally a collapsible blood bag topurge air from the receiving blood bag after filtration is complete.Also in any of the embodiments a means can be added to drain thebiological fluid in the tubing downstream of the BFFD into the receivingblood bag after the filtration cycle is complete, and then mix thebiological fluid in the receiving blood bag, and then express a quantityof mixed biological fluid back into the tubing downstream of the BFFD.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the detaileddescription of the preferred embodiments herein when read in conjunctionwith the drawings in which:

FIG. 1 is an isometric view of a first embodiment of a biological fluidfiltration system constructed in accordance with the principles of thepresent invention, usable for the filtration of biological fluids,containing a feed blood bag, a receiving blood bag, with the firstembodiment of a BFFD interposed between the feed blood bag and thereceiving blood bag, and with a three tube connector interposed betweenthe feed blood bag and the BFFD. A first vent filtration device isconnected to the three tube connector, and a second vent filtrationdevice is connected to the receiving blood bag;

FIG. 2 is a cross-sectional view of the first embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids;

FIG. 3 is an isometric view with portions thereof removed of the housingoutlet half of the BFFD shown in FIG. 2;

FIG. 4 is a top view of the housing outlet half of the BFFD shown inFIG. 2;

FIG. 5 is an isometric view of the housing inlet half of the BFFD shownin FIG. 2;

FIG. 6 is an isometric view with portions thereof removed of the threetube connector and the tubing connected to the three tube connector,shown in FIG. 1;

FIG. 7 is a top view of the body of a second embodiment of a three tubeconnector containing a built in loop;

FIG. 8 is an exploded isometric view with portions thereof removed of asecond embodiment of a three tube connector using the body shown in FIG.7;

FIG. 9 is an isometric view with portions thereof removed of a thirdembodiment of a three tube connector and the tubing connected to it;

FIG. 10 is an isometric view with portions thereof removed of a firstembodiment of a vent filtration device;

FIG. 11 is an isometric view with portions thereof removed of a secondembodiment of a vent filtration device;

FIG. 12 is an isometric view of a second embodiment of a biologicalfluid filtration system constructed in accordance with the principles ofthe present invention, usable for the filtration of biological fluids,containing a feed blood bag, a receiving blood bag, with a secondembodiment of a BFFD interposed between the feed blood bag and thereceiving blood bag. A first vent filtration device is connected to asecond inlet of the BFFD, and a second vent filtration device isconnected to the receiving blood bag;

FIG. 13 is a cross-sectional view of the second embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids;

FIG. 14 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 13;

FIG. 15 is a top view of the housing outlet half of the BFFD shown inFIG. 13;

FIG. 16 is an isometric view of the housing inlet half of the BFFD shownin FIG. 13;

FIG. 17 is a cross-sectional view of a third embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids, containing a diaphragmupstream of the BFFM. The third embodiment of the BFFD also contains arigid housing inlet half;

FIG. 18 is an isometric view with portions thereof removed of thehousing inlet half of the BFFD shown in FIG. 17;

FIG. 19 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 17;

FIG. 20 is a bottom isometric view with portions thereof removed of thediaphragm used in the BFFD shown in FIG. 17;

FIG. 21 is a top isometric view with portions thereof removed of thediaphragm used in the BFFD shown in FIG. 17;

FIG. 22 is a cross-sectional view of the BFFD shown in FIG. 17 with thediaphragm shown in the collapsed state after the filtration cycle iscomplete;

FIG. 23 is a cross-sectional view of a fourth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids, containing a diaphragmupstream of the BFFM. The fourth embodiment does not contain a rigidhousing inlet half;

FIG. 24 is a partial cross-sectional view of the BFFD shown in FIG. 23showing in greater detail the filter support screen;

FIG. 25 is an isometric view of the BFFD shown in FIG. 23;

FIG. 26 is an isometric view of the BFFD shown in FIG. 23 without thediaphragm;

FIG. 27 is a cross-sectional view of a fifth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids, containing a diaphragm,with the inlet located at the top of the housing. The fifth embodimentdoes not contain a rigid housing inlet half;

FIG. 28 is a cross-sectional view of the BFFD shown in FIG. 27 with thediaphragm shown in the collapsed state after the filtration cycle iscomplete;

FIG. 29 is a cross-sectional view of a sixth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids, containing a diaphragm,with the inlet located entirely below the chamber upstream of the BFFM;

FIG. 30 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 29;

FIG. 31 is an isometric view with portions thereof removed of thehousing inlet half of the BFFD shown in FIG. 29;

FIG. 32 is a cross-sectional view of the BFFD shown in FIG. 29 with thediaphragm shown in the collapsed state after filtration is complete;

FIG. 33 is a cross-sectional view of a seventh embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids, containing a diaphragm,with the inlet located at the bottom of the chamber upstream of theBFFM;

FIG. 34 is an isometric view of the housing inlet half of the BFFD shownin FIG. 33;

FIG. 35 is an isometric view of the diaphragm of the BFFD shown in FIG.33;

FIG. 36 is a cross-sectional view of an eighth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids. The eighth embodimentcontains a gel removing filter element, followed by a microaggregateremoving filter element, followed by a flow distribution filter element,followed by a leukocyte removing filter element that contains threelayers of porous filter material;

FIG. 37 is a partial cross-sectional view of the BFFD shown in FIG. 36;

FIG. 38 is a cross-sectional view of the housing outlet half of the BFFDshown in FIG. 36;

FIG. 39 is a cross-sectional view of the housing inlet half of the BFFDshown in FIG. 36;

FIG. 40 is a cross-sectional view of a ninth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids. The ninth embodimentcontains a gel removing filter element, followed by a microaggregateremoving filter element, followed by a first flow distribution filterelement, followed by a leukocyte removing filter element containingthree layers of leukocyte removing porous filter material, followed by asecond flow distribution filter element, followed by a particle trappingfilter element. The leukocyte removing filter element, and the secondflow distribution filter element, and the particle trapping filterelement all have a surface area less than the surface area of the gelfilter element, the microaggregate filter element, and the first flowdistribution filter element. The ninth embodiment also contains adiaphragm;

FIG. 41 is a partial cross-sectional view of the BFFD shown in FIG. 40without the second flow distribution filter element, and without theparticle trapping filter element, with a different sealing means beingused to seal the filter elements to the housing;

FIG. 42 is a partial cross-sectional view of the BFFD shown in FIG. 40with a different sealing means being used to seal the filter elements tothe housing;

FIG. 43 is a top view of the housing outlet half of the BFFD shown inFIG. 40;

FIG. 44 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 40;

FIG. 45 is a partial cross-sectional view of the BFFD shown in FIG. 40with a different sealing means being used to seal the filter elements tothe housing;

FIG. 46 is a cross-sectional view of a tenth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids. The tenth embodimentcontains a gel removing filter element, followed by a microaggregateremoving filter element, followed by a flow distribution filter element,followed by a leukocyte removing filter element, followed by a secondflow distribution filter element, followed by a particle trapping filterelement;

FIG. 47 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 46;

FIG. 48 is an isometric view of the housing inlet half of the BFFD shownin FIG. 46;

FIG. 49 is a cross-sectional view of an eleventh embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids. The BFFD shown in FIG.49 is double sided and uses variable surface area like the BFFD shown inFIG. 40;

FIG. 50 is a isometric view with portions thereof removed of the housingoutlet half of the BFFD shown in FIG. 49;

FIG. 51 is a top view of the housing outlet half of the BFFD shown inFIG. 49;

FIG. 52 is a partial cross-sectional view of the outlet portion of thehousing outlet half shown in FIG. 50;

FIG. 53 is a top view of the housing outlet half of the BFFD shown inFIG. 55;

FIG. 54 is a bottom view of the housing outlet half of the BFFD shown inFIG. 55;

FIG. 55 is a cross-sectional view of a twelfth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids. The BFFD shown in FIG.55 is double sided and uses variable surface area like the BFFD shown inFIG. 40. The BFFD shown in FIG. 55 also contains a vent inlet;

FIG. 56 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 55;

FIG. 57 is a cross-sectional view of a thirteenth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids. The BFFD shown in FIG.55 uses a flexible housing;

FIG. 58 is a cross-sectional view of the BFFD shown in FIG. 57 using adifferent method to seal the BFFM to the flexible housing;

FIG. 59 is a cross-sectional view of a fourteenth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids, and containing a gelremoving filter element, followed by a microaggregate removing filterelement, followed by a first flow distribution filter element, followedby a leukocyte removing filter element containing four layers ofleukocyte removing porous filter material;

FIG. 60 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 59;

FIG. 61 is an isometric view of a third embodiment of a biological fluidfiltration system constructed in accordance with the principles of thepresent invention, usable for the filtration of biological fluids,containing two feed blood bags, two receiving blood bags, with thefifteenth embodiment of a BFFD interposed between the two feed bloodbags and the two receiving blood bags, and with a single vent filtrationdevice connected to the first vent inlet and to the second vent inlet ofthe biological fluid filtration system via two separate lengths oftubing;

FIG. 62 is a cross-sectional view of the fifteenth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids;

FIG. 63 is a partial cross-sectional view of the BFFD shown in FIG. 62,rotated 180° about the central axis of the BFFD, showing the bottomoutlet of the BFFD;

FIG. 64 is a partial cross-sectional view of the BFFD shown in FIG. 62,showing the top outlet of the BFFD;

FIG. 65 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 62;

FIG. 66 is a top view of the housing outlet half of the BFFD shown inFIG. 62;

FIG. 67 is a bottom view of the housing outlet half of the BFFD shown inFIG. 62;

FIG. 68 is a partial top view of the housing outlet half of the BFFDshown in FIG. 62, showing the top outlet and the bottom outlet;

FIG. 69 is a top view of the housing body used in the vent filtrationdevice shown in FIG. 73;

FIG. 70 is an isometric view with portions thereof removed of thehousing body shown in FIG. 69;

FIG. 71 is an isometric view with portions thereof removed of thehousing cap used in the vent filtration device shown in FIG. 73;

FIG. 72 is an isometric view with portions thereof removed of analternate housing cap that can be used in the vent filtration deviceshown in FIG. 73;

FIG. 73 is an isometric view with portions thereof removed of the ventfiltration device used in the biological fluid filtration system shownin FIG. 61;

FIG. 74 is an isometric view with portions thereof removed of analternate vent filtration device that can be used in the biologicalfluid filtration system shown in FIG. 61;

FIG. 75 is a cross-sectional view of the sixteenth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids;

FIG. 76 is a partial cross-sectional view of the BFFD shown in FIG. 75,rotated 180° about the central axis of the BFFD, showing the bottomoutlet of the BFFD;

FIG. 77 is a partial cross-sectional view of the BFFD shown in FIG. 75,showing the top outlet of the BFFD;

FIG. 78 is an isometric view with portions thereof removed of the frontof the housing outlet half of the BFFD shown in FIG. 75;

FIG. 79 is an isometric view with portions thereof removed of the backof the housing outlet half of the BFFD shown in FIG. 75;

FIG. 80 is an isometric view of a fourth embodiment of a biologicalfluid filtration system constructed in accordance with the principles ofthe present invention, usable for the filtration of biological fluids,containing a feed blood bag, a receiving blood bag, with the eighteenthembodiment of a BFFD interposed between the feed blood bag and thereceiving blood bag, with a diaphragm draining device connected to athree tube connector containing a restriction, and with a single ventfiltration device connected to the vent outlet of the receiving bloodbag and to the flow path between the outlet of the BFFD and thereceiving blood bag;

FIG. 81 is a cross-sectional view of the eighteenth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids;

FIG. 82 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 81;

FIG. 83 is an isometric vie of the housing inlet half of the BFFD shownin FIG. 81;

FIG. 84 is a cross-sectional view of the diaphragm draining device shownin FIG. 80 with the diaphragm in its non-deflected state;

FIG. 85 is a cross-sectional view of the diaphragm draining device shownin FIG. 80 with the diaphragm in its deflected state;

FIG. 86 is a cross-sectional view of the inlet housing of diaphragmdraining device shown in FIG. 84 and FIG. 85;

FIG. 87 is a cross-sectional view of the outlet housing of diaphragmdraining device shown in FIG. 84 and FIG. 85;

FIG. 88 is a cross-sectional view of the diaphragm of diaphragm drainingdevice shown in FIG. 84 and FIG. 85;

FIG. 89 is a cross-sectional view of the three tube connector containinga restriction shown in FIG. 80;

FIG. 90 is an isometric view of the top of the housing cap used in thevent filtration device shown in FIG. 80;

FIG. 91 is an isometric view of the bottom of the housing cap used inthe vent filtration device shown in FIG. 80;

FIG. 92 is an isometric view of a fifth embodiment of a biological fluidfiltration system constructed in accordance with the principles of thepresent invention, usable for the filtration of biological fluids,containing a feed blood bag, a receiving blood bag, with the nineteenthembodiment of a BFFD interposed between the feed blood bag and thereceiving blood bag, with a vent filtration device connected to a threetube connector containing a restriction, and with a vent filtrationdevice connected to a tee below the outlet of the BFFD, and with a burpbag connected to the vent outlet of the receiving blood bag;

FIG. 93 is an isometric view with portions thereof removed of thehousing outlet half of the BFFD shown in FIG. 94;

FIG. 94 is a cross-sectional view of the seventeenth embodiment of aBFFD constructed in accordance with the principles of the presentinvention, usable for the filtration of biological fluids;

FIG. 95 is an isometric view of the seventeenth embodiment of a BFFDconstructed in accordance with the principles of the present invention,usable for the filtration of biological fluids;

FIG. 96 is a front view of the housing outlet half of the BFFD shown inFIG. 94;

FIG. 97 is a back view of the housing outlet half of the BFFD shown inFIG. 94.

DETAILED DESCRIPTION OF THE FIRST EMBODIMENT

Although various embodiments of the biological fluid filtration systemand the biological fluid filtration device (BFFD) constructed inaccordance with the principles of the present invention are disclosedherein, each embodiment minimizes the holdup of biological fluid in thebiological fluid filtration device (BFFD) after filtration is completeby incorporating filter support structures that minimize liquid holdupdownstream of the biological fluid filtration media (BFFM) used in thebiological fluid filtration device (BFFD), and by incorporating a meansto automatically drain the liquid upstream of the biological fluidfiltration media (BFFM) once filtration is complete; and each embodimentminimizes the amount of air that is purged from the BFFD afterbiological fluid starts to flow from the outlet of the BFFD.

One embodiment of the biological fluid filtration system constructed inaccordance with the principles of the present invention, is shown inFIG. 1 through FIG. 6, FIG. 10, and FIG. 11. Biological fluid filtrationsystem 1000 shown in FIG. 1 contains feed blood 98 and receiving bloodbag 99. Interposed between feed blood bag 98 and receiving blood bag 99is a biological fluid filtration device (BFFD) 100. Three tube connector50 is interposed between feed blood bag 98 and BFFD 100. First length oftubing 81 connects the outlet of feed blood bag 98 to first tube socket51 of three tube connector 50. Second length of tubing 81 a connectssecond tube socket 52 of three tube connector 50 to the inlet tubesocket 6 of BFFD 100. Third length of tubing 83 connects third tubesocket 53 of three tube connector 50 to tube socket 35 of ventfiltration device 30. A fourth length of tubing 82 connects outlet tubesocket 28 of BFFD 100 to the inlet of receiving blood bag 99. A fifthlength of tubing 84 connects a vent port on receiving blood bag 99 totube socket 45 of vent filtration device 40. Tubing 81 may contain tubeclamp 95, tubing 82 may contain tube clamp 96, tubing 84 may containtube clamp 97, and tubing 83 may contain tube clamp 94.

Referring to FIG. 2 through FIG. 5, BFFD 100 contains a rigid housingthat includes housing inlet half 1 and housing outlet half 20. Housingseal surface 29 a of housing inlet half 1 is bonded to housing sealsurface 29 of housing outlet half 20. The bond is preferably anultrasonic weld but may be a heat bond, a glue bond, a solvent bond, orany other type of leak tight bond.

Referring to FIG. 2 and FIG. 5 housing inlet half 1 contains filter well11 bounded by inner side wall 8 and by a plane that goes through filterseal surface 7. Upstream chamber 13 is bounded by inner wall 10 ofhousing inlet half 1 and by upstream surface 15 a of filter element 15.Upstream chamber 13 contains filter support ribs 9. Inlet 5 is in fluidflow communication with upstream chamber 13, via inlet slot 2. Theoutlet end of tubing 81 a is inserted into and bonded to inlet tubesocket 6. Inlet 5 and inlet slot 2 are shown located near the bottom ofupstream chamber 13 and on the vertical center line of housing inlethalf 1, they could however, be located anywhere between the top and thebottom of upstream chamber 13, and could also be located to the right orto the left of the vertical center line.

Referring to FIG. 2, FIG. 3, and FIG. 4 housing outlet half 20 containsvertical outlet channel 25 and outlet 27. Vertical outlet channel 25 isin direct fluid flow communication with outlet 27, and the portion ofvertical outlet channel 25 that adjoins outlet 27 has a cross-sectionalflow area that is greater than the cross-sectional flow area of outlet27. Housing outlet half 20 also contains horizontal collection channel26, a plurality of vertical channels 22, and a plurality of horizontalchannels 23. One end of each of the vertical and horizontal channels isin fluid flow communication with vertical outlet channel 25. Thevertical channels being in fluid flow communication with the verticaloutlet channel via the horizontal collection channel. The verticaloutlet channel, the horizontal collection channel, the verticalchannels, and the horizontal channels combined create a filter underdrain structure. The channels are cut into wall 37 of housing outlethalf 20 so that the inner surface of all of the channels lies belowinner wall 21 of housing outlet half 20 as shown in FIG. 3. The crosssectional area of the vertical outlet channel, the horizontal collectionchannel, the vertical channels, and the horizontal channels is definedby the inner surface of each channel and by the downstream surface ofthe BFFM. As shown in FIG. 2, FIG. 3, and FIG. 4, the distance betweenvertical channels 22 is much greater than the width of vertical channels22, and of the depth of vertical channels 22. The distance between thehorizontal channels 23 is much greater than the width of the horizontalchannels 23, and of the depth of horizontal channels 23. For example,the center line distance between the vertical channels and center linedistance between the horizontal channels may be equal to 0.150 in., withthe width of the vertical channels and the width of the horizontalchannels equal to 0.032 in., and with the depth of the vertical channelsand the depth of the horizontal channels equal to 0.025 in. As shown inFIG. 2, FIG. 3, and FIG. 4, the depth and width of the horizontalcollection channel (i.e. the cross-sectional area of the horizontalcollection channel) is sufficiently greater than that of the otherhorizontal channels to accommodate the flow of biological fluid from thevertical channels, through the horizontal collection channel, intooutlet channel 25, without creating an excessive pressure drop acrossthe horizontal collection channel. Housing outlet half 20 also containsfilter seal surface 24 and housing seal surface 29 both of which are apart of inner wall 21.

Referring to FIG. 2 and FIG. 3, a biological fluid filtration media(BFFM) that contains at least one filter element is interposed betweeninlet 5 and outlet 27, and is sealed to the housing to prevent the flowof unfiltered biological fluid from flowing between the housing and theBFFM to prevent bypass of unfiltered biological fluid around the BFFM.The BFFM shown in FIG. 2 contains filter elements 15, 16, 17, and 18.The filter elements may all be of the same type or may be differenttypes filter elements. Each filter element contains an upstream surfacedesignated as upstream surface 15 a for filter element 15, a downstreamsurface designated as downstream surface 15 c for filter element 15, anda perimeter surface designated as perimeter surface 15 b for filterelement 15. The downstream surface of the BFFM shown as downstreamsurface 18 c of filter element 18 is in contact with inner wall 21 ofhousing outlet half 20. Because the downstream surface of the BFFMcontacts inner wall 21 of housing outlet half 20, BFFD 100 does notcontain an open chamber or plenum downstream of the BFFM. The air orliquid that is forced through the BFFM must pass through the horizontaland vertical channels and the horizontal collection channel and theoutlet channel before flowing into outlet 27 of BFFD 100. The at leastone filter element may be sealed to the housing with an interference fitbetween perimeter surface of the filter element and inner side wall 8 ofhousing inlet half 1, or the at least one filter element may be sealedto the housing with a compression seal by compressing the outerperiphery of the at least one filter element between filter seal surface7 of housing inlet half 1 and filter seal surface 24 of housing outlethalf 20, or the at least one filter element may be sealed to the housinga heat seal, an ultrasonic weld, a glue seal, a solvent seal, a radiofrequency weld, or any other type of leak tight seal. A combination ofsealing methods may also be used to seal the at least one filter elementto the housing. For example, as shown in FIG. 2, the BFFM may be sealedto the housing a combination of an interference fit between perimetersurface of the at least one filter element and inner side wall 8 ofhousing inlet half 1, and a compression seal between the outer peripheryof the at least one filter element between filter seal surface 7 ofhousing inlet half 1 and filter seal surface 24 of housing outlet half20.

Referring to FIG. 2, a first fluid flow path is defined between inlet 5of BFFD 100 and outlet 27 of BFFD 100 with the at least one filterelement of the BFFM interposed between inlet 5 and outlet 27, and acrossthe fluid flow path. With the BFFM sealed to the housing to preventbypass of un-filtered biological fluid (i.e. liquid) around the BFFM.The first fluid flow path flows from inlet 5, through inlet slot 2, intoupstream chamber 13, through the at least one filter element of theBFFM, into the vertical channels 22, and into horizontal collectionchannel 26, and into the horizontal channels 23, into vertical outletchannel 25, and then into outlet 27.

Housing inlet half 1 may contain tube guide 3 to keep BFFD 100 hangingplumb when BFFD 100 is suspended from tubing 81 a as shown in FIG. 1.

Referring to FIG. 11 vent filtration device 30 contains a housingcomprised of housing cap 31 and housing body 32. The housing contains avent port 36 and a system port 34, with a first vent fluid flow pathdefined between vent port 36 and system port 34, with vent filtrationmedia 33 interposed between the vent port and the system port and acrossthe first vent fluid flow path. With the vent filtration media sealed tothe housing to prevent bypass of un-filtered gas (i.e. air) around thevent filtration media. The vent filtration media 33 is shown as a depthfilter media, such as a wad of cotton, a non-woven depth filtermaterial, a spun bound filter material, a molded porous filter materialor any other type of depth filter material. The vent filtration mediamay be hydrophobic or hydrophilic. Preferably vent filtration device 30is located above the liquid level in feed blood bag 98 as shown in FIG.1.

Vent filtration device 40 shown in FIG. 10 may be interchanged with ventfiltration device 30 shown in FIG. 11. Vent filtration device 40contains a housing comprised of housing cap 41 and housing body 42. Thehousing contains a vent port 46 and a system port 44, with a second ventfluid flow path defined between vent port 46 and system port 44, withvent filtration media 43 interposed between the vent port and the systemport and across the second vent fluid flow path. With the ventfiltration media sealed to the housing to prevent bypass of un-filteredgas (i.e. air) around the vent filtration media. The vent filtrationmedia 43 is shown as a microporous filter media such as a 0.2 μmmicroporous filter material, but may be any type of depth filter media,such as a non-woven depth filter material, a spun bound filter material,a molded porous filter material or any other type of depth filtermaterial. The vent filtration media may be hydrophobic or hydrophilic.Preferably vent filtration device 40 is located above the liquid levelin feed blood bag 98 as shown in FIG. 1.

Referring to FIG. 6 three tube connector 50 contains first tube socket51, second tube socket 52, and third tube socket 53. One end of tubing81 is connected to first tube socket 51, one end of tubing 81 a isconnected to second tube socket 52, and one end of tubing 83 isconnected to third tube socket 53. Three tube connector 50 containsfirst channel 54, second channel 55, and third channel 56. First channel54 may be referred to as inlet 54, second channel 55 may be referred toas outlet 55, and third channel 56 may be referred to as side port 56.Common node 57 (shown as a dot) places each of the three channels influid flow communication with the other two channels.

Referring to FIG. 1, FIG. 2, FIG. 6, and FIG. 11, a second fluid flowpath 58 is defined between feed blood bag 98 and common node 57 of threetube connector 50, with the flow in the second fluid flow path flowingfrom feed blood bag 98 through tubing 81, into first channel 54 of threetube connector 50, to the common node. A third fluid flow path 58 a isdefined between common node 57 of three tube connector 50 and inlet 5 ofBFFD 100, with the flow in the third fluid flow path flowing from commonnode 57 through tubing 81 a, to inlet 5 of BFFD 100. A portion of thethird fluid flow path is disposed above the common node. A fourth fluidflow path 59 is defined between the common node and atmosphere, with theflow of the fourth fluid flow path flowing from atmosphere, through ventport 36 of vent filtration device 30, through vent filtration media 33of vent filtration device 30, through system port 34 of vent filtrationdevice 30, through tubing 83, through third channel 56 of three tubeconnector 50, to the common node of three tube connector 50.

Referring to FIG. 1 and FIG. 10, biological fluid filtration system 1000may contain tubing 84 and vent filtration device 40. One end of tubing84 is connected to tube socket 45 of vent filtration device 40 and theother end of tubing 84 is connected to vent port 91 of receiving bloodbag 99. A fifth fluid flow path is defined from atmosphere to vent port91 of receiving blood bag 99. The fifth fluid flow path flows from ventport 46 of vent filtration device 40, through vent filtration media 43of vent filtration device 40, through system port 44 of vent filtrationdevice 40 through tubing 84, into vent port 91 of receiving blood bag99, when tube clamp 97 is open. Preferably vent filtration device 40 islocated above the liquid level in feed blood bag 98 as shown in FIG. 1.

Referring to FIG. 1, FIG. 6, and FIG. 11, biological fluid filtrationsystem 1000 functions as follows. The user will purchase the system withall components as shown in FIG. 1, less feed blood bag 98. The user willconnect tubing 81 to outlet 92 of feed blood bag 98 in a manner known inthe art. Feed blood bag 98, vent filtration device 30, and ventfiltration device 40 may be hung from a blood bag pole known in the art,and receiving blood bag 99 may be placed on a table top or the like, sothat the various components of the system will be positioned as shown inFIG. 1. Tube clamp 95 should be closed before connecting tubing 81 tofeed blood bag 98. Before opening tube clamp 95 to start the flow ofbiological fluid (i.e. liquid) through the system, tube clamps 94 and 96should be open, and tube clamp 97 should be closed. Referring to FIG. 1,FIG. 2, and FIG. 6, the distance L1 between the top of the liquid infeed blood bag 98 and common node 57 of three tube connector 50 must begreater than the distance L2 between common node 57 of three tubeconnector 50 and inlet 5 of BFFD 100.

The same fluid flow path designations that were used above will be usedin the following analysis. Referring to FIG. 1, FIG. 2, FIG. 6, and FIG.11, when tube clamp 95 is opened biological fluid (i.e. liquid) willflow through the second fluid flow path 58, from feed blood bag 98,through tubing 81, through first channel 54 of three tube connector 50to common node 57 of three tube connector 50. As biological fluid flowsfrom the feed blood bag towards the common node a portion of the air intubing 81 will be vented through vent filtration device 30, and theremainder of the air in tubing 81 will be forced into inlet 5 of BFFD100. Once biological fluid reaches the common node it will flow throughthe third fluid flow path 58 a from the common node, through secondchannel 55 of three tube connector 50, through tubing 81 a, into inlet 5of BFFD 100. If distance L1 from the top of the biological fluid in feedblood bag 98 to common node 57 of three tube connector 50 is greaterthan distance L2 from the common node to inlet 5 of BFFD 100, and if aportion of the third fluid flow path 58 a is located above the commonnode as shown in FIG. 1, then the pressure at the common node will bepositive, and a quantity of biological fluid will flow into tubing 83.The height of biological fluid in tubing 83 will be proportional to thevalue of the positive pressure at the common node, which is proportionalto the ratio of L1 to L2. Therefore air will be prevented from flowinginto the system from vent port 36 of vent filtration device 30 for alltime when biological fluid flows through the second fluid flow path 58,and for all time when biological fluid flows through the second fluidflow path 58 and through the third fluid flow path 58 a with tube clamp94 in the open position.

Referring to FIG. 1 through FIG. 5, BFFD 100 functions as follows.Biological fluid (i.e. liquid) flowing from tubing 81 a, will flowthrough the first fluid flow path by flowing into inlet 5 of BFFD 100,and then through inlet slot 2 of BFFD 100, into upstream chamber 13 ofBFFD 100. Upstream chamber 13 will rapidly fill with biological fluidfrom the bottom up. As upstream chamber 13 fills from the bottom up, theinitial air in upstream chamber 13 will be displaced by the biologicalfluid filling upstream chamber 13. The displaced air will be forcedthrough the BFFM, into vertical channels 22, and into horizontalchannels 23, and into horizontal collection channel 26, and intovertical outlet channel 25, and then into outlet 27 all of BFFD 100. Thebiological fluid in upstream chamber 13 will be pressurized, with thepressure at the bottom of upstream chamber 13 being proportional to thedistance from the top of the biological fluid in feed blood bag 98 tothe bottom of upstream chamber 13, and with the pressure at the top ofupstream chamber 13 being proportional to the distance from the top ofthe biological fluid in feed blood bag 98 to the top of upstream chamber13. Hence the pressure at the top of upstream chamber 13 will be lessthan the pressure at the bottom of upstream chamber 13. The positivepressure in upstream chamber 13 will cause the biological fluid to flowthrough the BFFM over the entire surface area of the BFFM and todisplace the air within the pores of the BFFM with biological fluid,thereby wetting BFFM from the upstream side 15 a of the BFFM to thedownstream side 18 c of the BFFM. As the BFFM wets the air that wasinitially in the pores of BFFM will be displaced by biological fluid andflow into vertical channels 22 and into horizontal channels 23, and intohorizontal collection channel 26, and into vertical outlet channel 25,and then into outlet 27 all of BFFD 100, into tubing 82, into receivingblood bag 99. Because the pressure at the bottom of upstream chamber 13is greater than the pressure at the top of upstream chamber 13, the flowrate of biological fluid through the BFFM will be greater at the bottomof the BFFM than at the top of the BFFM. Therefore, BFFM will firstbecome completely wetted from the upstream surface 15 a of BFFM todownstream surface 18 c of BFFM at the bottom of the BFFM. If the widthof vertical channels 22 is sufficiently small, and the depth of verticalchannels is sufficiently shallow, so that the cross-sectional flow areaof the vertical channels is sufficiently small, and if the distancebetween vertical channels is sufficiently large, as described above, thepath of least resistance for continued biological fluid flow through theBFFM will be through the capillaries of the BFFM in both the horizontaland vertical directions and not through the vertical channels, becauseif the cross-sectional flow area of the vertical channels issufficiently small, the displaced air flowing into and through thevertical channels will create a sufficiently high positive pressure inthe vertical channels to prevent biological fluid from entering thevertical channels. The downstream surface 18 c of the BFFM willtherefore wet from the bottom up and the displaced air that was withinthe BFFM will continue to flow into the vertical channels, and into thehorizontal collection channel, and into the horizontal channels, andinto the outlet channel, and then into the outlet. When the downstreamsurface of the BFFM has become wetted to the level of horizontalcollection channel 26, air flow through the vertical channels will stopbecause the downstream surface of the BFFM adjoining the verticalchannels will be wetted. Therefore the pressure in the vertical channelswill decrease allowing biological fluid to enter the vertical channelsfrom the bottom up, thereby displacing the air that was in the verticalchannels. At the same time the wetted level of the downstream surface ofthe BFFM will continue to wet in the vertical direction, wetting thedownstream surface of the BFFM adjoining horizontal collection channel26, and wetting the downstream surface of the BFFM adjoining the bottomof vertical outlet channel 25. Because neither the cross-sectional flowarea of horizontal collection channel 26, or the cross-sectional flowarea of vertical outlet channel 25 is sufficiently small to create asufficient positive pressure in them due to the air flow through them,biological fluid will flow into horizontal collection channel 26 andinto vertical outlet channel 25 as BFFM continues to wet in the verticaldirection above the bottom of horizontal collection channel 26. Thebiological fluid flowing into vertical channels 22 and into horizontalcollection channel 26 and into the bottom of vertical outlet channel 25will flow into outlet 27 of BFFD 100 and then into tubing 82 towardreceiving blood bag 99. As biological fluid starts to flow into outlet27, BFFM will continue to wet vertically, wetting first close to theouter perimeter of BFFM, and then toward the vertical outlet channel 25.Hence the initial flow of biological fluid into tubing 82 will consistof alternate segments of biological fluid and air. As will be seen inthe experimental data below, a BFFD constructed in accordance with theprinciples of the present invention, as shown in FIG. 2 through FIG. 5,will purge approximately 94% of the initial air in BFFD 100 beforebiological fluid begins to flow into outlet 27. To maximize the amountof air that is purged from BFFD 100 before biological fluid starts toflow into outlet 27, horizontal collection channel 26 should be locatedas high above the horizontal center line of BFFD 100 (and thereforeabove the horizontal centerline of the housing) as possible.

Referring to FIG. 1, when biological fluid starts to flow into tubing82, the pressure P downstream of the BFFM and upstream of outlet 27(i.e. downstream of the BFFM, but within BFFD 100) will be determined bythe following formula:P=L3−Δp−L4

-   -   Δp is the pressure drop across the BFFM due to biological fluid        flow through the BFFM.    -   L3 is the distance between outlet 27 of BFFD 100 and the top of        the biological fluid in feed blood bag 98.    -   L4 is the height of biological fluid minus any air segments        downstream of outlet 27, in tubing 82.        Therefore the pressure P within BFFD 100 and downstream of the        BFFM will be greater than or equal to zero until L4=L3−Δp. If        the bottom of horizontal collection channel 26 is positioned a        sufficient distance above the horizontal center line of BFFD        100, all of the air that was initially inside of BFFD 100 will        be purged from BFFD 100 before the pressure P within BFFD 100        downstream of the BFFM becomes negative. If however, the bottom        of horizontal collection channel 26 is positioned below the        horizontal center line of BFFD 100, all of the air that was        initially inside of BFFD 100 will not be purged from BFFD 100        before the pressure P within BFFD 100 downstream of the BFFM        becomes negative. As described above the pressure within        upstream chamber 13 of BFFD 100 will be positive as long as        biological fluid is flowing into upstream chamber 13. The        purging of air from within BFFD 100 is totally independent of        whether or not the pressure within BFFD 100 downstream of the        BFFM becomes negative. As will be seen in the experimental data        below, all of the air will be purged from within BFFD 100 even        if the pressure within BFFD 100 downstream of the BFFM never        becomes negative, as long as feed blood bag 98 is positioned a        sufficient distance above outlet 27 of BFFD 100.

If the flow rate through the BFFM is sufficiently small after the BFFMhas become completely wetted, the distance L1 from the top of thebiological fluid in feed blood bag 98 to common node 57 of three tubeconnector 50 may become less than distance L2 from the common node toinlet 5 of BFFD 100, without allowing air to enter into the system fromtubing 83, because the reduced flow rate through the BFFM will causebiological fluid to back up into tubing 83.

Referring to FIG. 1, FIG. 2, FIG. 6, and FIG. 11, once all of the airhas been purged from within BFFD 100, biological fluid will continue toflow through the first fluid flow path from the inlet of BFFD 100 to theoutlet of BFFD 100, and then through tubing 82 into receiving blood bag99 until feed blood bag 98 is emptied of biological fluid. At this pointfeed blood bag 98 will be collapsed, effectively sealing the top oftubing 81, thereby preventing the flow of biological fluid in the secondfluid flow path between the outlet of feed blood bag 98 and common node57 of three tube connector 50. With the second fluid flow path shut offas just described, air will now flow through the fourth fluid flow pathfrom vent port 36 of vent filtration device 30, through vent filtrationmedia 33, through system port 34, into tubing 83, thereby draining thebiological fluid in the fourth fluid flow path from system port 34 tocommon node 57 of three tube connector 50, and draining the biologicalfluid in the third fluid flow path from common node 57 to inlet 5 ofBFFD 100, and then draining the biological fluid in upstream chamber 13of BFFD 100. To complete the draining of biological fluid as justdescribed, receiving blood bag 99 must be positioned a sufficientdistance below outlet 27 of BFFD 100 to create a sufficiently negativepressure downstream of the BFFM and upstream of outlet 27 after all ofthe air has been purged from within BFFD 100 and tubing 82 is filledwith biological fluid, to create a sufficient pressure differentialbetween upstream surface 15 a and downstream surface 18 c of the BFFM todrain upstream chamber 13 to the bottom of upstream chamber 13, because,as the biological fluid level in upstream chamber 13 approaches thebottom of upstream chamber 13, the pressure on the bottom of thebiological fluid in upstream 13 will approach zero. When the filtrationcycle is complete, biological fluid will remain within the BFFM, and inthe filter under drain structure of housing outlet half 20, and intubing 82.

Referring to FIG. 1, when the filtration cycle is complete as justdescribed, the user will close tube clamp 96, and then cut and sealtubing 82 above tube clamp 96, and then discard BFFD 100 and theremaining components attached to it in a safe manner. Tubing 82 maycontain marks to divide it into segments. In this case tubing 82 wouldalso be sealed at each segment so that the biological fluid remaining ineach segment could be used for cross matching purposes Tube clamp 97 maynow be opened, and the air in receiving blood bag 99 may be purged fromreceiving blood bag 99 by squeezing receiving blood bag 99 therebyforcing the air in receiving blood bag 99 through the fifth fluid flowpath from vent port 91 of receiving blood bag 99 to atmosphere. Tubing84 can then be sealed and cut near receiving blood bag 99, and thentubing 84 and vent filtration device 40 may be discarded in a safemanner. Alternately a quantity of biological fluid from receiving bloodbag 99 may be squeezed into tubing 84 to be used for testing purposes,after the air is purged from the receiving blood bag. In this casetubing 84 may contain marks to divide it into segments. Tubing 84 wouldbe sealed above the level of biological fluid in it, and at each segmentmark, and then the portion of tubing 84 above the uppermost seal alongwith vent filtration device 40 would be cut away and discarded in a safemanner.

FIG. 7 and FIG. 8 show a second embodiment of the three tube connector.Three tube connector 50 a contains body 61, gasket 62, and cover 63.Body 61 contains first channel 54 a, second channel 55 a, third channel56 a, common node 57 a, first tube socket 51 a, second tube socket 52 a,and third tube socket 53 a. A portion of second channel 55 a ispositioned above common node 57 a. When the components of three tubeconnector 50 a are assembled, surface 67 of gasket 62 is in contact withsurface 64 of body 61, and surface 68 of gasket 62 is in contact withsurface 66 of cover 63, with the outer periphery of cover 63 sealed toflange 65 of body 61, thereby compressing gasket 62 between body 61 andcover 63, thereby creating closed channels 54 a, 55 a, and 56 a. Whenthree tube connector 50 a replaces three tube connector 50 in FIG. 1,tubing 81 is connected to first tube socket 51 a, tubing 83 is connectedto third tube socket 53 a, and tubing 81 a is connected to second tubesocket 52 a as shown in FIG. 8. Referring to FIG. 6 and FIG. 8, flowpath 58 aa of three tube connector 50 a replaces flow path 58 of threetube connector 50, flow path 58 aaa of three tube connector 50 areplaces flow path 58 a of three tube connector 50, and flow path 59 aof three tube connector 50 a replaces flow path 59 of three tubeconnector 50. Since a portion of flow path 58 aaa is positioned abovethe common node of three tube connector 50 a, there is no need to have aloop in tubing 81 a as shown in FIG. 1 (i.e. a straight length of tubing81 a from second tube socket 52 a of three tube connector 50 a to inlettube socket 6 of BFFD 100 can be used). Referring to FIG. 1, FIG. 2,FIG. 6, and FIG. 8, three tube connector 50 a without a loop in tubing81 a works the same as three tube connector 50 with a loop in tubing 81a, preventing air from entering the system during the filtration cycle,and draining tubing 83, tubing 81 a, and upstream chamber 13 of BFFD 100after the feed blood bag has emptied and flow stops through tubing 81,as described above.

FIG. 9 shows a third embodiment of the three tube connector. V-shapedthree tube connector 50 b contains first channel 54 b, second channel 55b, third channel 56 b, common node 57 b, first tube socket 51 b, secondtube socket 52 b, and third tube socket 53 b. When three tube connector50 b replaces three tube connector 50 in FIG. 1, tubing 81 is connectedto first tube socket 51 b, tubing 83 is connected to third tube socket53 b, and tubing 81 a is connected to second tube socket 52 b as shownin FIG. 9. Referring to FIG. 6 and FIG. 9, flow path 58 b of three tubeconnector 50 b replaces flow path 58 of three tube connector 50, flowpath 58 ab of three tube connector 50 b replaces flow path 58 a of threetube connector 50, and flow path 59 b of three tube connector 50 breplaces flow path 59 of three tube connector 50. Tubing 81 a as shownin FIG. 9 contains a loop with the central axis of portion of tubing 81a that goes from the three tube connector to the BFFD being parallel tothe central axis of tubing 81, thereby allowing the three tube connectorto hang plumb. As long as V-shaped three tube connector 50 b hangsplumb, it is not necessary to have a loop in tubing 81 a, since secondtube socket 52 b is located above the common node. Referring to FIG. 1,FIG. 2, FIG. 6, and FIG. 9, three tube connector 50 b with or without aloop in tubing 81 a works the same as three tube connector 50 with aloop in tubing 81 a, preventing air from entering the system during thefiltration cycle, and draining tubing 83, tubing 81 a, and upstreamchamber 13 of BFFD 100 after the feed blood bag has emptied, asdescribed above.

Other types of three tube connectors such as a tubing Y may also replacethe tubing Tee three tube connector shown in FIG. 1 and FIG. 6. The onlyrequirement for the three tube connector is that it place one end of theinterior of three lengths of tubing 81, 81 a, and 83, in fluid flowcommunication with each other.

Experimental Data of the First Embodiment

Experimental data was obtained by testing a machined BFFD constructed asshown in FIG. 2, FIG. 3, FIG. 4, and FIG. 5. The machined BFFD used aBFFM consisting of nine layers of 2.6 inch diameter by 0.030 inch thickfibrous filtration material. The BFFM was sealed to the housing aninterference fit between the perimeter surface of the BFFM and thehousing, and by compressing the outer periphery of the upstream surfaceof the BFFM and the outer periphery of the downstream surface of theBFFM between a filter seal surface on the housing inlet half and afilter seal surface on the housing outlet half, as shown in FIG. 2.

To determine how the air was purged from the BFFD the inlet of the BFFDwas connected to an open top reservoir located above the BFFD with aball valve located between the reservoir and the inlet of the BFFD, andthe outlet of the BFFD was connected to a length of tubing with an openend. The distance L3 shown in FIG. 1 between the top of the fluid in thereservoir and the outlet of the BFFD was 21 inch. The test fluid wasun-filtered tap water. A test hole was drilled and tapped through thehousing outlet half through center line 93 shown in FIG. 2. One end of awater manometer was connected to the test hole to measure the pressure P(defined above) within the BFFD downstream of the BFFM and upstream ofthe outlet of the BFFD.

In the first test the reservoir was filled with un-filtered tap water sothat L3 shown in FIG. 1 was 21 inches. The outlet tubing was heldhorizontal a the level of the outlet of the BFFD. The ball valve wasopened allowing the un-filtered tap water to flow from the reservoir tothe inlet of the BFFD. The BFFD filled, and wetted the BFFM and purgedall of the air from within the BFFD just as described in the detaileddescription of the first embodiment above. The pressure P as measured bythe manometer was zero until liquid started to flow downstream of theBFFM into the outlet tubing. At this point the pressure became positiveand remained positive. The outlet end of the outlet tubing was thenslowly lowered. As the outlet end of the outlet tubing was lowered, thepressure P decreased and became zero when the outlet end of the outlettubing was 15½ inches below the outlet of the BFFD. From the equationP=L3−Δp−L4, defined above, substituting zero for P, we have Δp=L3−L4, orin the experiment just described, Δp=21−15.5=5.5 in. H₂O. Therefore, forthe conditions just described, the pressure P downstream of the BFFM andupstream of the outlet of the BFFD will be greater than or equal to zerofor all time until the length of a column of water, either a continuouswater column, or the sum of the length of the water segments in a columnconsisting of alternate water-air segments, equals 15½ inches. This testwas repeated several times yielding the same results.

To determine the quantity of air that is purged from the BFFD afterliquid starts to flow from the outlet of the BFFD the inlet of the BFFDwas connected to an open top reservoir located above the BFFD with aball valve located between the reservoir and the inlet of the BFFD, andthe outlet of the BFFD was connected to a length of tubing with an openend. The distance L3 shown in FIG. 1 between the top of the fluid in thereservoir and the outlet of the BFFD was 21 inch. The test fluid wasun-filtered tap water. The test hole was sealed.

In the second test the reservoir was filled with un-filtered tap waterso that L3 shown in FIG. 1 was 21 inches. The outlet tubing was heldhorizontal at the level of the outlet of the BFFD. The ball valve wasopened allowing the un-filtered tap water to flow from the reservoir tothe inlet of the BFFD. The BFFD filled, and wetted the BFFM and purgedall of the air from within the BFFD just as described above in thedetailed description of the first embodiment above. After all of the airwas purged from the BFFD, the ball valve was closed to stop flow and thelength of the column of alternate segments of air and liquid in theoutlet tubing was measured. This was done several times, with the lengthof the column of alternate segments of air and liquid in the outlettubing varying between 10 inches and 15 inches, with approximately halfof the column consisting of air with the remainder being water. Hence,the column of liquid in the outlet tubing varied between 5 inches and7.5 inches at the point when all of the air had been purged from theBFFD. For this device the first experiment shows that it takes a columnof water 15.5 inches high in the outlet tubing to make the pressure Pequal to zero, and the second experiment shows that the column of wateris 5 inches to 7.5 inches high when all of the air has been purged fromthe BFFD. Therefore, all of the air is purged from the BFFD before thepressure P becomes negative, so that a negative pressure P is not usedto purge air from the BFFD. Furthermore, the first experiment shows thatall of the air in the BFFD will be purged from the BFFD for conditionswhere the pressure P remains positive throughout the filtration cycle(i.e. the outlet tubing was held at the level of centerline 93 shown inFIG. 2). Therefore purging the air from the downstream side of the BFFMwithin the housing does not depend on a negative pressure downstream ofthe BFFM. For the above conditions, if the outlet tubing is positionedbelow the outlet, than when the length of the liquid column in theoutlet tube exceeds 15.5 inches the negative pressure downstream of theBFFM will increase the total pressure available to force liquid throughthe BFFM, and therefore decrease the filtration time, but will have noeffect on weather or not air is purged from downstream of the BFFMwithin the housing.

To verify the performance of the three tube connector shown in FIG. 1and FIG. 6, the following third test was performed. A tubing tee asshown in FIG. 1 and FIG. 6 was used for the three tube connector.Referring to FIG. 1, an open top reservoir was used in place of feedblood bag 98, and the outlet end of tubing 81 a was open to atmosphere,with the open end positioned below the common node of the tubing tee andwith a portion of tubing 81 a positioned above the common node of thetubing tee as shown in FIG. 1. The vent filtration device 30 waspositioned above the top of the liquid level in the open top reservoiras shown in FIG. 1. The liquid was un-filtered tap water. The BFFD andthe receiving blood bag were not used. A ball valve was used in place oftube clamp 95. At the start of the experiment the distance between theopen end of tubing 81 a and the common node of the tubing tee was lessthan the distance between the common node of the tubing tee and the topof the liquid in the reservoir. When the ball valve was opened to startliquid flow, water flowed from the reservoir through tubing 81 andthrough tubing 81 a to the outlet end of tubing 81 a, with a quantity ofwater flowing into tubing 83, indicating that the pressure at the commonnode of the tubing tee was positive as explained above in the detaileddescription of the first embodiment. The open end of tubing 81 a wasthen slowly lowered while observing the liquid level in tubing 83. Asthe open end of tubing 81 a was lowered, the liquid level in tubing 83receded toward the common node of the tubing tee. When the open end oftubing 81 a was lowered to the point that the distance between the openend of tubing 81 a and the common node of the tubing tee was equal tothe distance between the common node of the tubing tee and the top ofthe liquid in the reservoir, all of the liquid had receded from tubing83. When the open end of tubing 81 a was lowered further so thatdistance between the open end of tubing 81 a and the common node of thetubing tee was greater than the distance between the common node of thetubing tee and the top of the liquid in the reservoir, air began to flowinto the tubing tee from tubing 83, and then flow into tubing 81 a. Theopen end of tubing 81 a was then raised so that the distance between theopen end of tubing 81 a and the common node of the tubing tee was equalto the distance between the common node of the tubing tee and the top ofthe liquid in the reservoir, at which point air stopped flowing into thetubing tee from tubing 83. When the open end of tubing 81 a was raisedfurther, water started to flow into tubing 83 indicating a positivepressure at the common node of the tubing tee. This experimental dataconfirms the detailed description of the three tube connector above.

The third test was repeated using the three tube connector shown in FIG.7 and FIG. 8 to replace the tubing tee shown in FIG. 1 and FIG. 6. Theresults were the same as the results of the third test.

A fourth test was performed as follows: Referring to FIG. 1, FIG. 2, andFIG. 6, a tubing tee was used for the three tube connector with aportion of tubing 81 a positioned above the common node of the tee asshown in FIG. 1. An open top reservoir was used in place of feed bloodbag 98, and the outlet end of tubing 81 a was connected to the inlet ofthe BFFD used in the first and second tests above, with the outlet endof tubing 82 open to atmosphere. A ball valve was used in place of tubeclamp 95. The distance L1 from the bottom of the reservoir to the commonnode of the tubing tee was greater than the distance from the commonnode of the tubing tee to the inlet of the BFFD. Vent filtration device30 was positioned above the top of the liquid in the reservoir as shownin FIG. 1. When the ball valve was opened to allow un-filtered tap waterto flow from the reservoir, water flowed from the reservoir throughtubing 81 and through tubing 81 a into the inlet of the BFFD, with aquantity of water flowing into tubing 83, thereby preventing air fromentering the tee from tubing 83. The BFFD filled, and wetted the BFFMand purged all of the air from within the BFFD just as described in thedetailed description of the first embodiment above. Liquid flowcontinued from the reservoir, through the BFFD, into tubing 82 until theball valve was closed to simulate feed blood bag 98 emptying and thencollapsing. Once liquid flow was stopped in tubing 81, air enteredtubing 83 through vent filtration device 30, thereby draining the liquidin tubing 83, and the liquid in tubing 81 a, and the liquid in thetubing tee between tubing 83 and tubing 81 a, and the liquid in upstreamchamber 13 of the BFFD just as described in the detailed description ofthe first embodiment above.

Detailed Description of the Second Embodiment

A second embodiment of the biological fluid filtration systemconstructed in accordance with the principles of the present invention,is shown in FIG. 10 through FIG. 16. Biological fluid filtration system2000 shown in FIG. 12 contains feed blood 98 and receiving blood bag 99.Interposed between feed blood bag 98 and receiving blood bag 99 is abiological fluid filtration device (BFFD) 200. First length of tubing 81connects the outlet of feed blood bag 98 to the inlet tube socket 106 ofBFFD 200. A second length of tubing 82 connects outlet tube socket 128of BFFD 200 to the inlet of receiving blood bag 99. Third length oftubing 85 connects vent tube socket 179 of BFFD 200 to tube socket 45 ofvent filtration device 40. A fourth length of tubing 84 connects a ventport on receiving blood bag 99 to tube socket 35 of vent filtrationdevice 30. Tubing 81 may contain tube clamp 95, tubing 82 may containtube clamp 96, tubing 84 may contain tube clamp 97, and tubing 85 maycontain tube clamp 94.

Referring to FIG. 13, BFFD 200 contains a rigid housing that includeshousing inlet half 101 and housing outlet half 120. Housing seal surface129 a of housing inlet half 101 is bonded to housing seal surface 129 ofhousing outlet half 120. The bond is preferably an ultrasonic weld butmay be a heat bond, a glue bond, a solvent bond, or any other type ofleak tight bond.

Referring to FIG. 13 and FIG. 16 housing inlet half 101 containsupstream chamber 113 that is bounded by inner wall 110 of housing inlethalf 101 and by upstream surface 15 a of filter element 15. Upstreamchamber 113 contains filter support ribs 109. Inlet 105 is in fluid flowcommunication with upstream chamber 113, via inlet slot 102. The outletend of tubing 81 is inserted into and bonded to inlet tube socket 106.Inlet 105 and inlet slot 102 are shown located near the top of upstreamchamber 113 and on the vertical center line of housing inlet half 101,they could however, be located anywhere between the top and the bottomof upstream chamber 113, and could also be located to the right or tothe left of the vertical center line. Housing inlet half 101 alsocontains vent inlet 178, and vent inlet slot 177. One end of tubing 85is inserted into and bonded to vent tube socket 179. Vent inlet 178 andvent inlet slot 177 are shown located near the bottom of upstreamchamber 113 and on the vertical center line of housing inlet half 101,they could however, be located anywhere between the top and the bottomof upstream chamber 113, and could also be located to the right or tothe left of the vertical center line.

Referring to FIG. 13, FIG. 14, and FIG. 15 housing outlet half 120contains filter well 111 bounded by inner side wall 108 and by a planethat goes through filter seal surface 124. Housing outlet half alsocontains circular outlet channel 125 and outlet 127. Circular outletchannel 125 is in direct fluid flow communication with outlet 127, andthe portion of circular outlet channel 125 that adjoins outlet 127 has across-sectional flow area that is greater than the cross-sectional flowarea of outlet 127. Housing outlet half 120 also contains a plurality ofopen top closed bottom vertical channels 122 and 122 a. One end of eachof the vertical channels 122 and 122 a is in fluid flow communicationwith circular outlet channel 125. The upper part of circular outletchannel 125 increases in width to accommodate the flow of biologicalfluid from vertical channels 122 and 122 a. The width of the remainderof circular outlet channel 125 (i.e. the lower part of circular outletchannel 125) is preferably equal to the width of the vertical channels.Preferably the upper part of circular outlet channel 125 is also deeperthan the lower part of circular outlet channel 125 as shown in FIG. 13.However, the upper part of circular outlet channel 125 may increase indepth, or increase in width, or both, from its outer edges toward thecenter of circular outlet channel 125, so that its cross-sectional areawill increase to accommodate the flow from all of the vertical channelswithout creating an excessive pressure drop through circular outletchannel 125. The two outermost vertical channels designated as verticalchannels 122 a adjoin circular outlet channel 125 where the width ofcircular outlet channel 125 is equal to the width of the verticalchannels. The circular outlet channel and the vertical channelscombined, create a filter under drain structure. The circular outletchannel and the vertical channels are cut into wall 137 of housingoutlet half 120 so that the inner surface of all of the channels liesbelow inner wall 121 of housing outlet half 120 as shown in FIG. 14. Thecross sectional area the outlet channel and of the vertical channels isdefined by the inner surface of each channel and by the downstreamsurface of the BFFM. As shown in FIG. 14 and FIG. 15, the distancebetween vertical channels 122 and 122 a is much greater than the widthof vertical channels 122 and 122 a; and the distance between verticalchannels 122 and 122 a is also much greater than the depth of verticalchannels 122 and 122 a. For example, the center line distance betweenthe vertical channels may be equal to 0.150 in., with the width of thevertical channels equal to 0.032 in., and with the depth of the verticalchannels equal to 0.025 in. Circular outlet channel 125 may containfilter support ribs 123. Housing outlet half 120 also contains fitterseal surface 124. Housing outlet half 120 may contain tube guide 103 tokeep BFFD 200 hanging plumb when BFFD 200 is suspended from tubing 81 asshown in FIG. 12. Because housing outlet half 120 does not contain anopen chamber or plenum downstream of the BFFM, hold up volume ofbiological fluid is minimized.

Referring to FIG. 13 through FIG. 16, a biological fluid filtrationmedia (BFFM) that contains at least one filter element is interposedbetween inlet 105 and outlet 127, and is sealed to the housing toprevent the flow of unfiltered biological fluid from flowing between thehousing and the BFFM to prevent bypass of unfiltered biological fluidaround the BFFM. The BFFM shown in FIG. 13 contains filter elements 15,16, 17, and 18. The filter elements may all be of the same type or maybe different types filter elements. Each filter element contains anupstream surface designated as upstream surface 15 a for filter element15, a downstream surface designated as downstream surface 15 c forfilter element 15, and a perimeter surface designated as perimetersurface 15 b for filter element 15. The downstream surface of the BFFMshown as downstream surface 18 c of filter element 18 is in contact withinner wall 121 of housing outlet half 120. Because the downstreamsurface of the BFFM contacts inner wall 121 of housing outlet half 120,BFFD 200 does not contain an open chamber or plenum downstream of theBFFM. The air or liquid that is forced through the BFFM must passthrough vertical channels and the circular outlet channel before flowinginto outlet 127 of BFFD 200. The at least one filter element may besealed to the housing with an interference fit between the perimetersurface of the filter element and inner side wall 108 of housing outlethalf 120, or the at least one filter element may be sealed to thehousing with a compression seal by compressing the outer periphery ofthe at least one filter element between filter seal surface 107 ofhousing inlet half 101 and filter seal surface 124 of housing outlethalf 120, or the at least one filter element may be sealed to thehousing a heat seal, an ultrasonic weld, a glue seal, a solvent seal, aradio frequency weld (i.e. R.F. weld), or any other type of leak tightseal. A combination of sealing methods may also be used to seal the atleast one filter element to the housing. As shown in FIG. 13, filterelement 15 has an outside diameter smaller than the inside diameter ofinner side wall 108 of housing outlet half 120 preventing filter element15 from being sealed to BFFD 200 with an interference fit between theperimeter surface 15 b of filter element 15 and inner side wall 108 ofhousing outlet half 120. The outer periphery of filter element 15 issealed to the housing by compressing the outer periphery of upstreamsurface 15 a of filter element 15 with filter seal surface 107 ofhousing inlet half 101. Filter elements 16, 17, and 18 are shown sealedto the housing with an interference fit between the perimeter surface ofeach respective filter element and inner side wall 108 of housing outlethalf 120. In addition the outer periphery of the BFFM comprised offilter elements 15, 16, 17, and 18, is compression sealed between filterseal surface 107 of housing inlet half 101, and filter seal surface 124of housing outlet half 120.

Referring to FIG. 13 a first fluid flow path is defined between inlet105 of BFFD 200 and outlet 127 of BFFD 200 with the at least one filterelement of the BFFM interposed between inlet 105 and outlet 127, andacross the fluid flow path (i.e. the BFFM is sealed to the housing toprevent the flow of un-filtered biological fluid between the BFFM andthe housing thereby preventing bypass of un-filtered biological fluidaround the BFFM). The first fluid flow path flows from inlet 105,through inlet slot 102, into upstream chamber 113, through the at leastone filter element of the BFFM, into vertical channels 122, intocircular outlet channel 125, and then into outlet 127.

Referring FIG. 12 vent filtration device 30 and vent filtration device40 are the same vent filtration devices used in biological fluidfiltration system 1000, and may be interchanged as was the case inbiological fluid filtration system 1000.

Referring to FIG. 10 and FIG. 12 biological fluid filtration system 2000may contain tubing 85 and vent filtration device 40. One end of tubing85 is connected to tube socket 45 of vent filtration device 40 and theother end of tubing 85 is connected to vent tube socket 179 of BFFD 200.A second fluid flow path for biological fluid filtration system 2000 isdefined from atmosphere to vent inlet 178 of BFFD 200. The second fluidflow path for biological fluid filtration system 2000 flows from ventport 46 of vent filtration device 40, through vent filtration media 43of vent filtration device 40, through system port 44 of vent filtrationdevice 40 through tubing 85, into vent inlet 178 of BFFD 200, when tubeclamp 94 is open. Preferably vent filtration device 40 is located abovethe liquid level in feed blood bag 98 as shown in FIG. 12.

Referring to FIG. 11 and FIG. 12 biological fluid filtration system 2000may contain tubing 84 and vent filtration device 30. One end of tubing84 is connected to tube socket 35 of vent filtration device 30 and theother end of tubing 84 is connected to vent port 91 of receiving bloodbag 99. A third fluid flow path for biological fluid filtration system2000 is defined from atmosphere to vent port 91 of receiving blood bag99. The third fluid flow path for biological fluid filtration system2000 flows from vent port 36 of vent filtration device 30, through ventfiltration media 33 of vent filtration device 30, through system port 34of vent filtration device 30 through tubing 84, into vent port 91 ofreceiving blood bag 99, when tube clamp 97 is open. Preferably ventfiltration device 30 is located above the liquid level in feed blood bag98 as shown in FIG. 12.

Referring to FIG. 12, biological fluid filtration system 2000 functionsas follows. The user will purchase the system with all components asshown in FIG. 12, less feed blood bag 98. The user will connect tubing81 to outlet 92 of feed blood bag 98 in a manner known in the art. Feedblood bag 98, vent filtration device 30, and vent filtration device 40may be hung from a blood bag pole known in the art, and receiving bloodbag 99 may be placed on a table top or the like, so that the variouscomponents of the system will be positioned as shown in FIG. 12. Tubeclamp 95 should be closed before connecting tubing 81 to feed blood bag98. Before opening tube clamp 95 to start the flow of biological fluidthrough the system, tube clamps 94 and 96 should be open, and tube clamp97 should be closed.

Referring to FIG. 12 through FIG. 16, BFFD 200 functions as follows.When tube clamp 95 is opened biological fluid (i.e. liquid) will flowfrom feed blood bag 98, through tubing 81, into inlet 105 of BFFD 200,and then through inlet slot 102 of BFFD 200, into upstream chamber 113of BFFD 200. Upstream chamber 113 will rapidly fill with biologicalfluid from the bottom up. As upstream chamber 113 fills from the bottomup, the initial air in upstream chamber 113 will be displaced by thebiological fluid filling upstream chamber 113. The displaced air will beforced through the BFFM, into vertical channels 122 and 122 a, intocircular outlet channel 125, and then into outlet 127 all of BFFD 200.The biological fluid in upstream chamber 113 will be pressurized, withthe pressure at the bottom of upstream chamber 113 being proportional tothe distance from the top of the biological fluid in feed blood bag 98to the bottom of upstream chamber 113, and with the pressure at the topof upstream chamber 113 being proportional to the distance from the topof the biological fluid in feed blood bag 98 to the top of upstreamchamber 113. Hence the pressure at the top of upstream chamber 113 willbe less than the pressure at the bottom of upstream chamber 113. Thepositive pressure in upstream chamber 113 will cause the biologicalfluid to flow through the BFFM over the entire surface area of the BFFMand to displace the air within the pores of the BFFM with biologicalfluid, thereby wetting BFFM from the upstream side 15 a of the BFFM tothe downstream side 18 c of the BFFM. As the BFFM wets the air that wasinitially in the pores of BFFM will be displaced by biological fluid andflow into vertical channels 122 and 122 a, and into circular outletchannel 125, and than into outlet 127 all of BFFD 200, into tubing 82,and then into receiving blood bag 99. Because the pressure at the bottomof upstream chamber 113 is greater than the pressure at the top ofupstream chamber 113, the flow rate of biological fluid through the BFFMwill be greater at the bottom of the BFFM than at the top of the BFFM.Therefore, BFFM will first become completely wetted from the upstreamsurface 15 a of BFFM to downstream surface 18 c of BFFM at the bottom ofthe BFFM. If the width of vertical channels 122 and 122 a issufficiently small, and the depth of vertical channels 122 and 122 a issufficiently shallow, so that the cross-sectional flow area of verticalchannels 122 and 122 a is sufficiently small, and if the distancebetween vertical channels 122 is sufficiently large, as described above,the path of least resistance for continued biological fluid flow throughthe BFFM will be through the capillaries of the BFFM in both thehorizontal and vertical directions and not through the verticalchannels, because if the cross-sectional flow area of the verticalchannels is sufficiently small, the displaced air flowing into andthrough the vertical channels will create a sufficiently high positivepressure in the vertical channels to prevent biological fluid fromentering the vertical channels. The downstream surface 18 c of the BFFMwill therefore wet from the bottom up and the displaced air that waswithin the BFFM will continue to flow into the vertical channels, andinto the circular outlet channel, and then into the outlet. When thedownstream surface of the BFFM has become wetted to the level of theupper part of circular outlet channel 125 where circular outlet channel125 begins to taper to a wider width, air flow through the lower part ofcircular outlet channel 125, and air flow through the two outermostvertical channels 122 a will stop because the downstream surface of theBFFM adjoining the lower part of the circular outlet channel and the twooutermost vertical channels will be wetted. Therefore the pressure inthe lower part of the circular outlet channel and the pressure in thetwo outermost vertical channels will decrease allowing biological fluidto enter the lower part of the circular outlet channel and the twooutermost vertical channels from the bottom up, thereby displacing theair that was in the lower part of the circular outlet channel and thetwo outermost vertical channels. At the same time the wetted level ofthe downstream surface of the BFFM will continue to wet in the verticaldirection, wetting the downstream surface of the BFFM adjoining theupper part of circular outlet channel 125. Because the cross-sectionalflow area of the upper part of circular outlet channel 125 is notsufficiently small to create a positive pressure in it due to the airflow through it, biological fluid will begin to into vertical channels122 and into circular outlet channel 125 as BFFM continues to wet in thevertical direction above the lower part of the circular outlet channel.The biological fluid flowing into vertical channels 122 and 122 a, andinto the circular outlet channel 125 will flow into outlet 127 of BFFD200 and then into tubing 82 toward receiving blood bag 99. As biologicalfluid starts to flow into outlet 127. BFFM will continue to wetvertically. Hence the initial flow of biological fluid through the upperpart of circular outlet channel 125, and through outlet 127, will be amixture of air and biological fluid so that the initial flow into tubing82 will consist of alternate segments of biological fluid and air. Aswill be seen in the experimental data below, a BFFD constructed inaccordance with the principles of the present invention, as shown inFIG. 12 through FIG. 16, will purge approximately 98% of the initial airin BFFD 200 before biological fluid begins to flow into outlet 127.

Referring to FIG. 12 and FIG. 13, when biological fluid starts to flowinto tubing 82, the pressure P1 downstream of the BFFM and upstream ofoutlet 127 (i.e. downstream of the BFFM, but within BFFD 200) will bedetermined by the following formula:P1=L5Δp−L6

-   -   Δp is the pressure drop across the BFFM due to biological fluid        flow through the BFFM.    -   L5 is the distance between outlet 127 of BFFD 200 and the top of        the biological fluid in feed blood bag 98.    -   L6 is the height of biological fluid minus any air segments        downstream of outlet 127, in tubing 82.        Therefore the pressure P1 within BFFD 200 and downstream of the        BFFM will be greater than or equal to zero until L6=L5−Δp.        Because the upper part of circular outlet channel 125 is located        a sufficient distance above the horizontal center line of BFFD        200, all of the air will be purged from within BFFD 200 before        the pressure P1 becomes negative. As described above the        pressure within upstream chamber 113 of BFFD 200 will be        positive as long as biological fluid is flowing into upstream        chamber 113. The purging of air from within BFFD 200 is only        dependent upon the positive pressure upstream of the BFFM and is        totally independent of whether or not the pressure within BFFD        200 downstream of the BFFM becomes negative. As will be seen in        the experimental data below, all of the air will be purged from        within BFFD 200 even if the pressure within BFFD 200 downstream        of the BFFM never becomes negative, as long as feed blood bag 98        is positioned a sufficient distance above outlet 127 of BFFD        200.

Referring to FIG. 10, FIG. 12, and FIG. 13, a once all of the air hasbeen purged from within BFFD 200, biological fluid will continue to flowthrough the first fluid flow path from the inlet of BFFD 200 to theoutlet of BFFD 200, and then through tubing 82 into receiving blood bag99 until feed blood bag 98 is emptied of biological fluid. At this pointfeed blood bag 98 will be collapsed, effectively sealing the top oftubing 81, thereby preventing the flow of biological fluid in tubing 81.With flow through tubing 81 shut off as just described, air will nowflow through the second fluid flow path from vent port 46 of ventfiltration device 40, through vent filtration media 43, through systemport 44, through tubing 85, through vent inlet 178, through vent inletslot 177, and then into upstream chamber 113, all of BFFD 200, therebydraining the biological fluid in upstream chamber 113 of BFFD 200. Tocomplete the draining of biological fluid as just described, receivingblood bag 99 must be positioned a sufficient distance below outlet 127of BFFD 200 to create a sufficiently negative pressure P1 downstream ofthe BFFM and upstream of outlet 127 after all of the air has been purgedfrom within BFFD 200 and tubing 82 is filled with biological fluid, tocreate a sufficient pressure differential between upstream surface 15 aand downstream surface 18 c of the BFFM to drain upstream chamber 113 tothe bottom of upstream chamber 113, because as the biological fluidlevel in upstream chamber 113 approaches the bottom of upstream chamber113, the pressure on the bottom of the biological fluid in upstream 113will approach zero.

Referring to FIG. 12, FIG. 13, and FIG. 15, when the filtration cycle iscomplete as just described, the BFFM will remain wetted, verticalchannels 122 and 122 a, and circular outlet channel 125 will be filledwith biological fluid, and tubing 82 will be filled with biologicalfluid. Because BFFD 200 does not contain a plenum downstream of theBFFM, the hold up volume of biological fluid within BFFD 200 will beminimized. The user will close tube clamp 96, and then cut and sealtubing 82 above tube clamp 96, and then discard BFFD 200 and theremaining components attached to it in a safe manner. Tubing 82 maycontain segment marks, in which case tubing 82 would also be sealed atthe segment marks. The biological fluid in the segments would be usedfor cross-matching purposes. Tube clamp 97 may nom/be opened, and theair in receiving blood bag 99 may be purged from receiving blood bag 99by squeezing receiving blood bag 99 thereby forcing the air in receivingblood bag 99 through the third fluid flow path from vent port 91 ofreceiving blood bag 99 to atmosphere. Tubing 84 can then be sealed andcut near receiving blood bag 99, and then tubing 84 and vent filtrationdevice 30 may be discarded in a safe manner. Alternately tubing 84 couldalso contain segment marks. In this case the biological fluid inreceiving blood bag 99 would be mixed before opening tube clamp 97. Tubeclamp 97 would then be opened, and the air in receiving blood bag 99purged from receiving blood bag 99 by squeezing receiving blood bag 99thereby forcing the air in receiving blood bag 99 through the thirdfluid flow path from vent port 91 of receiving blood bag 99 toatmosphere. Once the air is purged from receiving blood bag 99 aquantity of biological fluid would also be purged into tubing 84. Tubing84 can then be sealed near receiving blood bag 99 and at the segmentmarks, and then the portion of tubing 84 above the seals and ventfiltration device 30 may be discarded in a safe manner. The biologicalfluid in the segments could be used to test the filtered biologicalfluid.

Experimental Data of the Second Embodiment

Experimental data was obtained by testing a machined BFFD constructed asshown in FIG. 13, FIG. 14, FIG. 15, and FIG. 16. The machined BFFD useda BFFM consisting of nine layers of fibrous filtration material of 2.6inch diameter, 0.030 inch thick. The BFFM was sealed to the housing aninterference fit between the perimeter surface of the BFFM and thehousing, and by compressing the outer periphery of the upstream surfaceof the BFFM and the outer periphery of the downstream surface of theBFFM between a filter seal surface on the housing inlet half and afilter seal surface on the housing outlet half, as shown in FIG. 13.

To determine how the air was purged from the BFFD the inlet of the BFFDwas connected to an open top reservoir located above the BFFD with aball valve located between the reservoir and the inlet of the BFFD, andthe outlet of the BFFD was connected to a length of tubing with an openend. The distance L5 shown in FIG. 12 between the top of the fluid inthe reservoir and the outlet of the BFFD was 21 inch. The test fluid wasun-filtered tap water. A test hole was drilled and tapped through thehousing outlet half through center line 193 shown in FIG. 13. One end ofa water manometer was connected to the test hole to measure the pressureP1 (defined above) within the BFFD downstream of the BFFM and upstreamof the outlet of the BFFD.

In the first test the reservoir was filled with un-filtered tap water sothat L5 shown in FIG. 12 was 21 inches. The outlet tubing was heldhorizontal a the level of the outlet of the BFFD. The ball valve wasopened allowing the un-filtered tap water to flow from the reservoir tothe inlet of the BFFD. The BFFD filled, and wetted the BFFM and purgedall of the air from within the BFFD just as described in the detaileddescription of the second embodiment above. The pressure P1 as measuredby the manometer was zero until liquid started to flow downstream of theBFFM into the outlet tubing. At this point the pressure became positiveand remained positive. The outlet end of the outlet tubing was thenslowly lowered. As the outlet end of the outlet tubing was lowered, thepressure P1 decreased and became zero when the outlet end of the outlettubing was 15½ inches below the outlet of the BFFD. From the equationP1=L5−Δp−L6, defined above, substituting zero for P1, we have Δp=L5−L6,or in the experiment just described, Δp=21−15.5=5.5 in. H₂O. Therefore,for the conditions just described, the pressure P1 downstream of theBFFM and upstream of the outlet of the BFFD will be greater than orequal to zero for all time until the length of a column of water, eithera continuous water column, or the sum of the length of the watersegments in a column consisting of alternate water-air segments, equals15½ inches. This test was repeated several times yielding the sameresults.

To determine the quantity of air that is purged from the BFFD afterliquid starts to flow from the outlet of the BFFD the inlet of the BFFDwas connected to an open top reservoir located above the BFFD with aball valve located between the reservoir and the inlet of the BFFD, andthe outlet of the BFFD was connected to a length of tubing with an openend. The distance L5 shown in FIG. 12 between the top of the fluid inthe reservoir and the outlet of the BFFD was 21 inch. The test fluid wasun-filtered tap water. The test hole was sealed.

In the second test the reservoir was filled with un-filtered tap waterso that L5 shown in FIG. 12 was 21 inches. The outlet tubing was heldhorizontal a the level of the outlet of the BFFD. The ball valve wasopened allowing the un-filtered tap water to flow from the reservoir tothe inlet of the BFFD. The BFFD filled, and wetted the BFFM and purgedall of the air from within the BFFD just as described in the detaileddescription of the second embodiment above. After all of the air waspurged from the BFFD, the ball valve was closed to stop flow and thelength of the column of alternate segments of air and liquid in theoutlet tubing was measured. This was done several times, with the lengthof the column of alternate segments of air and liquid in the outlettubing varying between 4 inches and 5 inches, with approximately half ofthe column consisting of air with the remainder being water. Hence, thecolumn of liquid in the outlet tubing varied between 2 inches and 2.5inches at the point when all of the air had been purged from the BFFD.For this device the first experiment shows that it takes a column ofwater 15.5 inches high in the outlet tubing to make the pressure P1equal to zero, and the second experiment shows that the column of wateris 2 inches to 2.5 inches high when all of the air has been purged fromthe BFFD. Therefore, all of the air is purged from the BFFD before thepressure P1 becomes negative, so that a negative pressure P1 is not usedto purge air from the BFFD. Furthermore, the first experiment shows thatall of the air in the BFFD will be purged from the BFFD for conditionswhere the pressure P1 remains positive throughout the filtration cycle.The inside diameter of the tubing used was 0.3 cm. It takes a length Las shown in the following equation of this diameter tubing to equal aninternal volume of 1 cc.L*((Π*0.3 cm²)/4)=1 cm³=1 mlL=14.2 cm=5.6 inTherefore, essentially all of the air is purged from a BFFD constructedaccording to FIG. 13, FIG. 14, FIG. 15, and FIG. 16, after only ½ of 1ml of liquid has flowed from of the outlet of the BFFD.

Bed Side Applications of the Second Embodiment

Because essentially all of the air is purged from a BFFD constructedaccording to FIG. 13, FIG. 14, FIG. 15, and FIG. 16, after only ½ of 1ml of liquid has flowed from of the outlet of the BFFD, this type ofBFFD is ideally suited for bed side applications. Referring to FIG. 12,in a bed side application where blood or blood product is beingtransfused, receiving blood bag 99, tubing 84, vent filtration device30, and tube clamp 97 would be eliminated, and the outlet end of tubing82 would be connected to a drip chamber, with the outlet of the dripchamber connected to the patient. During priming the drip chamber isinverted and blood flows from the feed blood bag through tubing 81,through BFFD 200, through tubing 82 (as described above), and then intothe drip chamber. When 3 to 4 ml of blood or blood product has beencollected in the drip chamber, it is returned to its normal position,leaving a reservoir of fluid in the bottom of the drip chamber and anair space above the fluid. The transparent drip chamber allowsobservation of the drip rate through the air space, and prevents any airthat may be purged from the BFFD after the drip chamber has beenreturned to its normal position from reaching the patient. This laggingair will displace an equivalent amount of fluid from the drip chamber.Because essentially all of the air in the BFFD will be purged before 3to 4 ml of fluid is collected in the drip chamber as described above, asmall drip chamber may be used without the concern that lagging air willdrain the drip chamber and reach the patient, therefore minimizingwasted biological fluid. The hold up volume of vertical channels 122 and122 a, and of circular outlet channel 125 is less than the hold upvolume of a plenum. Therefore, the hold up volume of BFFD 200 is furtherreduced because BFFD 200 does not contain a plenum downstream of theBFFM.

A BFFD containing the filter support structure of BFFD 100 could also beused in biological fluid filtration system 2000. Likewise a BFFDcontaining the filter support structure of BFFD 200 could also be usedin biological fluid filtration system 1000.

Detailed Description of the Third Embodiment

A third embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 17 through FIG.21. BFFD 300 may be used in place of BFFD 100 in biological fluidfiltration system 1000 shown in FIG. 1, and may also be used in place ofBFFD 200 in biological fluid filtration system 2000 shown in FIG. 12.

Referring to FIG. 17, FIG. 18, and FIG. 19, BFFD 300 contains a rigidhousing that includes housing inlet half 201 and housing outlet half220. Housing seal surface 229 a of housing inlet half 201 is bonded tohousing seal surface 229 of housing outlet half 220. The bond ispreferably an ultrasonic weld but may be a heat bond, a glue bond, asolvent bond, or any other type of leak tight bond.

Referring to FIG. 17, FIG. 18, FIG. 20, and FIG. 21, housing inlet half201 contains filter well 211 bounded by inner side wall 208 and by aplane that goes through diaphragm seal surface 207. Housing inlet half201 also contains diaphragm well 209 bounded by surface 210. Diaphragmwell 209 contains hole 271. Flexible diaphragm 260 contains innersurface 263, outer surface 266, and flange 262. The outer surface offlange 262 is sealed to diaphragm seal surface of housing inlet half201. The seal may be a heat seal, an ultrasonic seal, a glue seal, asolvent seal, or any other type of leak tight seal. Flexible diaphragm260 may be molded from a flexible rubber material such as siliconerubber, or it may be molded or thermo formed from a material such asPVC, polyethylene, or polypropylene, but is not limited to thesematerials. Flexible diaphragm 260 is preferably shaped so that in itsnormal state outer surface 266 conforms to surface 210 of housing inlethalf 201. Flexible diaphragm 260 also contains tube connector 261, thatcontains inlet tube socket 206, and inlet 205. Tube connector 261loosely fits through hole 271 of housing inlet half 201. Upstreamchamber 213 is bounded by inner surface 263 of flexible diaphragm 260and by upstream surface 15 a of filter element 15. Inlet 205 is in fluidflow communication with upstream chamber 213. When BFFD 300 is used inbiological fluid filtration system 1000 shown in FIG. 1, the outlet endof tubing 81 a is inserted into and bonded to inlet tube socket 206.When BFFD 300 is used in biological fluid filtration system 2000 shownin FIG. 12, the outlet and of tubing 81 is inserted into and bonded toinlet tube socket 206. Inlet 205 is shown located near the bottom ofupstream chamber 213 and on the vertical center line of housing inlethalf 201, it could however be located anywhere between the top and thebottom of upstream chamber 213, and could also be located to the rightor to the left of the vertical center line of housing inlet half 201.

Referring to FIG. 17, and FIG. 19 housing outlet half 220 containscircular outlet channel 225 and outlet 227. Circular outlet channel 225is in direct fluid flow communication with outlet 227, and the portionof circular outlet channel 225 that adjoins outlet 227 has across-sectional flow area that is greater than the cross-sectional flowarea of outlet 227. Housing outlet half 220 also contains a plurality ofopen top closed bottom vertical channels 222 and 222 a. One end of eachof the vertical channels 222 and 222 a is in fluid flow communicationwith circular outlet channel 225. The upper part of circular outletchannel 225 increases in width to accommodate the flow of biologicalfluid from vertical channels 222 and 222 a. The width of the remainderof circular outlet channel 225 (i.e. the lower part of circular outletchannel 225) is preferably equal to the width of the vertical channels.The two outermost vertical channels designated as vertical channels 222a adjoin circular outlet channel 225 where the width of circular outletchannel 225 is equal to the width of the vertical channels. The outletchannel and the vertical channels that combined create a filter underdrain structure, are cut into wall 237 of housing outlet half 220 sothat the inner surface of all of the channels lies below inner wall 221of housing outlet half 220 as shown in FIG. 19. The cross sectional areathe outlet channel and of the vertical channels is defined by the innersurface of each channel and by the downstream surface of the BFFM. Asshown in FIG. 19, the distance between vertical channels 222 and 222 ais much greater than the width of vertical channels 222 and 222 a, andthe distance between vertical channels 222 and 222 a is also muchgreater than the depth of vertical channels 222 and 222 a. For example,the center line distance between the vertical channels may be equal to0.150 in., with the width of the vertical channels equal to 0.032 in.,and with the depth of the vertical channels equal to 0.025 in. Housingoutlet half 220 also contains filter seal surface 224. Because housingoutlet half 220 does not contain an open chamber or plenum downstream ofthe BFFM, hold up volume of biological fluid will be minimized.

Referring to FIG. 17, a biological fluid filtration media (BFFM) thatcontains at least one filter element is interposed between inlet 205 andoutlet 227, and is sealed to the housing to prevent the flow ofunfiltered biological fluid from flowing between the housing and theBFFM to prevent bypass of unfiltered biological fluid around the BFFM.The BFFM shown in FIG. 17 contains filter elements 15, 16, 17, and 18.The filter elements may all be of the same type or may be differenttypes filter elements. Each filter element contains an upstream surfacedesignated as upstream surface 15 a for filter element 15, a downstreamsurface designated as downstream surface 15 c for filter element 15, anda perimeter surface designated as perimeter surface 15 b for filterelement 15. The downstream surface of the BFFM shown as downstreamsurface 18 c of filter element 18 is in contact with inner wall 221 ofhousing outlet half 220. Because the downstream surface of the BFFMcontacts inner wall 221 of housing outlet half 220, BFFD 300 does notcontain an open chamber or plenum downstream of the BFFM. The air orliquid that is forced through the BFFM must pass through the verticalchannels and the circular outlet channel before flowing into outlet 227of BFFD 300. The at least one filter element may be sealed to thehousing with an interference fit between the perimeter surface of the atleast one filter element and inner side wall 208 of housing inlet half201, or the at least one filter element may be sealed to the housingwith a compression seal by compressing the outer periphery of the atleast one filter element between the inner surface of flange 262 offlexible diaphragm 260 and filter seal surface 224 of housing outlethalf 220, or the at least one filter element may be sealed to thehousing a heat seal, an ultrasonic weld, a glue seal, a solvent seal, aradio frequency weld, or any other type of leak tight seal. Acombination of sealing methods may also be used to seal the at least onefilter element to the housing.

Referring to FIG. 17 a first fluid flow path is defined between inlet205 of BFFD 300 and outlet 227 of BFFD 300 with the at least one filterelement of the BFFM interposed between inlet 205 and outlet 227, andacross the fluid flow path. The first fluid flow path flows from inlet205, into upstream chamber 213, through the at least one filter elementof the BFFM, into vertical channels 222 and 222 a, into circular outletchannel 225, and then into outlet 227.

Referring to FIG. 12 and FIG. 17, when BFFD 300 is used to replace BFFD200 in biological fluid filtration system 2000, the system will functionas follows. The user will purchase the system with all components asshown in FIG. 12, less feed blood bag 98. BFFD 300 will replace BFFD200, tubing 85 and vent filtration device 40 will not be used. The userwill connect tubing 81 to outlet 92 of feed blood bag 98 in a mannerknown in the art. Feed blood bag 98 and vent filtration device 30, maybe hung from a blood bag pole known in the art, and receiving blood bag99 may be placed on a table top or the like. Tube clamp 95 should beclosed before connecting tubing 81 to feed blood bag 98. Before openingtube clamp 95 to start the flow of biological fluid through the system,tube clamp 96 should be open, and tube clamp 97 should be closed.

Referring to FIG. 12, FIG. 17, and FIG. 19, BFFD 300 functions asfollows. When tube clamp 95 is opened biological fluid (i.e. liquid)will flow from feed blood bag 98, through tubing 81, into inlet 205 ofBFFD 300 and then into upstream chamber 213 of BFFD 300. Upstreamchamber 213 will rapidly fill with biological fluid from the bottom up.As upstream chamber 213 fills from the bottom up, the initial air inupstream chamber 213 will be displaced by the biological fluid fillingupstream chamber 213. The displaced air will be forced through the BFFM,into vertical channels 222 and 222 a, into circular outlet channel 225,and then into outlet 227 all of BFFD 300. The biological fluid inupstream chamber 213 will be pressurized, with the pressure at thebottom of upstream chamber 213 being proportional to the distance fromthe top of the biological fluid in feed blood bag 98 to the bottom ofupstream chamber 213, and with the pressure at the top of upstreamchamber 213 being proportional to the distance from the top of thebiological fluid in feed blood bag 98 to the top of upstream chamber213. Hence the pressure at the top of upstream chamber 213 will be lessthan the pressure at the bottom of upstream chamber 213. The positivepressure in upstream chamber 213 will cause the biological fluid to flowthrough the BFFM over the entire surface area of the BFFM and todisplace the air within the pores of the BFFM with biological fluid,thereby wetting BFFM from the upstream side 15 a of the BFFM to thedownstream side 18 c of the BFFM. As the BFFM wets the air that wasinitially in the pores of BFFM will be displaced by biological fluid andflow into vertical channels 222 and 222 a, and into circular outletchannel 225, and then into outlet 227 all of BFFD 300, into tubing 82,and then into receiving blood bag 99. Because the pressure at the bottomof upstream chamber 213 is greater than the pressure at the top ofupstream chamber 213, the flow rate of biological fluid through the BFFMwill be greater at the bottom of the BFFM than at the top of the BFFM.Therefore, the BFFM will first become completely wetted from upstreamsurface 15 a of the BFFM to downstream surface 18 c of the BFFM, at thebottom of the BFFM. If the width of vertical channels 222 and 222 a issufficiently small, and the depth of vertical channels 222 and 222 a issufficiently shallow, so that the cross-sectional flow area of verticalchannels 222 and 222 a is sufficiently small, and if the distancebetween vertical channels 222 and 222 a is sufficiently large, asdescribed above, the path of least resistance for continued biologicalfluid flow through the BFFM will be through the capillaries of the BFFMin both the horizontal and vertical directions and not through thevertical channels, because if the cross-sectional flow area of thevertical channels is sufficiently small, the displaced air flowing intoand through the vertical channels will create a sufficiently highpositive pressure in the vertical channels to prevent biological fluidfrom entering the vertical channels. The downstream surface 18 c of theBFFM will therefore wet from the bottom up and the displaced air thatwas within the BFFM will continue to flow into the vertical channels,and into the circular outlet channel, and then into the outlet. When thedownstream surface of the BFFM has become wetted to the level of theupper part of circular outlet channel 225 where circular outlet channel225 begins to taper to a wider width, air flow through the lower part ofcircular outlet channel 225, and air flow through the two outermostvertical channels 222 a will stop because the downstream surface of theBFFM adjoining the lower part of the circular outlet channel and the twooutermost vertical channels will be wetted. Therefore the pressure inthe lower part of the circular outlet channel and the pressure in thetwo outermost vertical channels will decrease allowing biological fluidto enter the lower part of the circular outlet channel and the twooutermost vertical channels from the bottom up, thereby displacing theair that was in the lower part of the circular outlet channel and thetwo outermost vertical channels. At the same time the wetted level ofthe downstream surface of the BFFM will continue to wet in the verticaldirection, wetting the downstream surface of the BFFM adjoining theupper part of circular outlet channel 225. Because the cross-sectionalflow area of the upper part of circular outlet channel 225 is notsufficiently small to create a positive pressure in it due to the airflow through it, biological fluid will flow into circular outlet channel225 as BFFM continues to wet in the vertical direction above the lowerpart of the circular outlet. The biological fluid flowing into verticalchannels 222 and 222 a, and into circular outlet channel 225 will flowinto outlet 227 of BFFD 300 and then into tubing 82 toward receivingblood bag 99. As biological fluid starts to flow into outlet 227, theBFFM will continue to wet vertically. Hence the initial flow ofbiological fluid through the upper part of circular outlet channel 225,and through outlet 227, will be a mixture of air and biological fluid sothat the initial flow into tubing 82 will consist of alternate segmentsof biological fluid and air. From the experimental data of the secondembodiment described above, a BFFD constructed in accordance with theprinciples of the present invention, as shown in FIG. 17 through FIG.21, will purge approximately 98% of the initial air in BFFD 300 beforebiological fluid begins to flow into outlet 227.

Referring to FIG. 12 and FIG. 17, when biological fluid starts to flowinto tubing 82, the pressure P2 downstream of the BFFM and upstream ofoutlet 227 (i.e. downstream of the BFFM, but within BFFD 300) will bedetermined by the following formula:P2=L5−Δp−L6

-   -   Δp is the pressure drop across the BFFM due to biological fluid        flow through the BFFM.    -   L5 is the distance between outlet 227 of BFFD 300 and the top of        the biological fluid in feed blood bag 98.    -   L6 is the height of biological fluid minus any air segments        downstream of outlet 227, in tubing 82.        Therefore the pressure P2 within BFFD 300 and downstream of the        BFFM will be greater than or equal to zero until L6=L5−Δp.        Because the upper part of circular outlet channel 225 is located        a sufficient distance above the horizontal center line of BFFD        300, all of the air will be purged from within BFFD 300 before        the pressure P2 becomes negative. As described above the        pressure within upstream chamber 213 of BFFD 300 will be        positive as long as biological fluid is flowing into upstream        chamber 213. The purging of air from within BFFD 300 is totally        independent of whether or not the pressure within BFFD 300        downstream of the BFFM becomes negative as explained above.

Referring to FIG. 12, and FIG. 17 through FIG. 22, once all of the airhas been purged from within BFFD 300, biological fluid will continue toflow through the first fluid flow path from the inlet of BFFD 300 to theoutlet of BFFD 300, and then through tubing 82 into receiving blood bag99 until feed blood bag 98 is emptied of biological fluid. At this pointfeed blood bag 98 will be collapsed, effectively sealing the top oftubing 81, thereby preventing the flow of biological fluid in tubing 81.If receiving blood bag 99 is positioned at a level that is sufficientlylower than BFFD 300, pressure P2 downstream of the BFFM and upstream ofoutlet 227 will be negative as described above. Once feed blood bag 98collapses and biological fluid flow through the first fluid flow pathstops the differential pressure across the BFFM will become zero, hencethe pressure in upstream chamber 213 will become negative. The pressureon upstream surface 266 of flexible diaphragm 260 will be atmosphericbecause hole 271 of housing inlet half 201 is open to atmosphere. Withatmospheric pressure on the outer surface 266 of flexible diaphragm 260,the negative pressure within upstream chamber 213 will cause flexiblediaphragm 260 to collapse onto upstream surface 15 a of the BFFM asshown in FIG. 22, thereby forcing the biological fluid in upstreamchamber 213 through the BFFM, into the vertical channels and thecircular outlet channel, into outlet 227, into tubing 82, and then intoreceiving blood bag 99.

Referring to FIG. 12, FIG. 17, and FIG. 19, when the filtration cycle iscomplete as just described, the BFFM will remain wetted, verticalchannels 222 and 222 a, and circular outlet channel 225 will be filledwith biological fluid, and tubing 82 will be filled with biologicalfluid. Because BFFD 300 does not contain a plenum downstream of theBFFM, the hold up volume of biological fluid within BFFD 300 will beminimized. The user will close tube clamp 96, and then cut and sealtubing 82 above tube clamp 96, and then discard BFFD 300 and feed bloodbag 98 in a safe manner. Tube clamp 97 may now be opened, and the air inreceiving blood bag 99 may be purged from receiving blood bag 99 bysqueezing receiving blood bag 99 thereby forcing the air in receivingblood bag 99 through the third fluid flow path from vent port 91 ofreceiving blood bag 99 to atmosphere. Tubing 84 can then be sealed andcut near receiving blood bag 99, and then tubing 84 and vent filtrationdevice 30 may be discarded in a safe manner. If tubing 82 and 84 containsegment marks, then the procedure described in the second embodimentconcerning the segment marks may be used.

BFFD 300 can be used to replace BFFD 100 in biological fluid filtrationsystem 1000 shown in FIG. 1. If BFFD 300 is used in this manner, it willpurge air and filter biological fluid as just described. Three tubeconnector 50 and vent filtration device 30 will function as described inthe description of the first embodiment above. When the filtration cycleis complete, tubing 83, tubing 81 a, and upstream chamber 213 of BFFD300 will drain as described in the description of the first embodimentabove, and flexible diaphragm 260 will remain in the un-collapsed state.

Detailed Description of the Fourth Embodiment

A fourth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 23 through FIG.26. BFFD 400 may be used in place of BFFD 100 in biological fluidfiltration system 1000 shown in FIG. 1, and may also be used in place ofBFFD 200 in biological fluid filtration system 2000 shown in FIG. 12.

Referring to FIG. 14, FIG. 20, FIG. 21, FIG. 23, and FIG. 24, BFFD 400contains a rigid housing outlet half 120 a, and flexible diaphragm 260.BFFD 400 lacks a rigid housing inlet half. Housing outlet half 120 a isthe same as housing outlet half 120, with the following exceptions.Housing outlet half 120 a contains counter bore 126, and tube guide 103a of housing outlet half 120 a replaces tube guide 103 of housing outlethalf 120. The inner surface of flange 262 of flexible diaphragm 260 issealed to housing seal surface 129 of housing outlet half 120 a. Theseal may be a heat seal, an ultrasonic seal, a glue seal, a solventseal, or any other type of leak tight seal. The BFFM shown in FIG. 23contains filter elements 15, 16, and 17. The filter elements may all beof the same type or may be different types filter elements. The BFFMmust contain at least one filter element. The at least one filterelement may be sealed to the housing with an interference fit betweenthe perimeter surface of the filter element and inner side wall 108 ofhousing outlet half 120 a, or the at least one filter element may besealed to the housing with a compression seal by compressing the outerperiphery of the at least one filter element between the inner surfaceof flange 262 of flexible diaphragm 260 and filter seal surface 124 ofhousing outlet half 120 a, or the at least one filter element may besealed to the housing a heat seal, an ultrasonic weld, a glue seal, asolvent seal, a radio frequency weld, or any other type of leak tightseal. A combination of sealing methods may also be used to seal the atleast one filter element to the housing. Upstream chamber 313 is definedbetween the inner surface 263 of flexible diaphragm 260, and upstreamsurface 15 a of the BFFM. BFFD 400 may also contain filter supportscreen 70. Filter support screen 70 does not perform a filtrationfunction but acts as a filter support and containment mechanism similarto filter support ribs 9 of housing inlet half 1 shown in FIG. 5.Therefore filter support screen 70 can have a very open structure asshown in FIG. 26. Preferably filter support screen 70 fits into counterbore 126 of housing inlet half 120 a, and is bonded to the housing inlethalf, or compressed between flange 262 of flexible diaphragm 260 andhousing inlet half 120 a. Tubing 81 may be bonded to tube guide 103 a torelieve strain on flexible diaphragm 260 when BFFD 400 is suspended fromtubing 81.

BFFD 400 works exactly as BFFD 300 when used in either biological fluidfiltration system 1000, or in biological fluid filtration system 2000 asdescribed above in the description of the third embodiment of the BFFD.

Detailed Description of the Fifth Embodiment

A fifth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 27 and FIG. 28.BFFD 500 contains rigid housing outlet half 120 b and flexible diaphragm460. Housing outlet half 120 b is the same as housing outlet half 120 awith the following exceptions. Housing outlet half 120 b does notcontain a tube guide, and housing outlet half 120 b contains inlet 105b, and inlet tube socket 106 b both located at the top of housing outlethalf 120 b. Flexible diaphragm 460 is the same as flexible diaphragm 260with the exception that flexible diaphragm 460 does not contain a tubeconnector with an inlet. Upstream chamber 413 is bounded by the innersurface of flexible diaphragm 460 and by the upstream surface 15 a ofthe BFFM. Inlet 105 b is in fluid flow communication with upstreamchamber 413 as shown in FIG. 27. BFFD 500 may contain filter supportscreen 70 bonded to housing outlet half 120 b.

BFFD 500 may be used in place of BFFD 100 in biological fluid filtrationsystem 1000 shown in FIG. 1, and may also be used in place of BFFD 200in biological fluid filtration system 2000 shown in FIG. 12. BFFD 500works exactly as BFFD 300 when used in either biological fluidfiltration system 1000, or in biological fluid filtration system 2000 asdescribed above in the description of the third embodiment of the BFFD.FIG. 28 shows flexible diaphragm 460 in the collapsed state after thefiltration cycle has been completed.

Detailed Description of the Sixth Embodiment

A sixth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 29 through FIG.31. BFFD 600 contains a rigid housing that includes housing inlet half501 and housing outlet half 520. Housing seal surface 529 a of housinginlet half 501 is bonded to housing seal surface 529 of housing outlethalf 520. The bond is preferably an ultrasonic weld but may be a heatbond, a glue bond, a solvent bond, or any other type of leak tight bond.

Referring to FIG. 29, and FIG. 31 housing inlet half 501 containsdiaphragm well 509 bounded by surface 510. Hole 571 goes through wall512 and is in fluid flow communication with circular vent channels 503and radial vent channel 503 a. Flexible diaphragm 560 contains innersurface 563, outer surface 566, and flange 562. The outer surface offlange 562 is sealed to diaphragm seal surface 507 of housing inlet half501. The seal may be a heat seal, an ultrasonic seal, a glue seal, asolvent seal, or any other type of leak tight seal. Alternately flange562 may be sealed to the housing by compressing flange 562 betweendiaphragm seal surface 507 of housing inlet half 501 and diaphragm sealsurface 507 a of housing outlet half 520. In which case diaphragm sealsurface 507 a should be an un-interrupted surface like filter sealsurface 907 shown in FIG. 48, and second inlet slot 502 a should beformed like slot 904 a shown in FIG. 48. Flexible diaphragm 560 may bemolded from a flexible rubber material such as silicone rubber, or itmay be molded or thermo formed from a material such as PVC,polyethylene, or polypropylene, but is not limited to these materials.Flexible diaphragm 560 is preferably shaped so that in its normal stateouter surface 566 conforms to surface 510 of housing inlet half 501.Housing inlet half 501 also contains inlet 505, first inlet slot 502,and inlet tube socket 506. Upstream chamber 513 is bounded by innersurface 563 of flexible diaphragm 560, and by surface 508 a of housingoutlet half 520, and by upstream surface 15 a of filter element 15.Inlet 505 is in fluid flow communication with upstream chamber 513through first inlet slot 502. When BFFD 600 is used in biological fluidfiltration system 1000 shown in FIG. 1, the outlet end of tubing 81 a isinserted into and bonded to inlet tube socket 506. Inlet 505 is locatedbelow the bottom of upstream chamber 513 and on the vertical center lineof housing inlet half 501. When BFFD 600 is used in biological fluidfiltration system 2000 shown in FIG. 12, the outlet end of tubing 81 isinserted into and bonded to inlet tube socket 506.

Referring to FIG. 29, and FIG. 30 housing outlet half 520 contains thesame filter under drain structure that was used in the second embodimentdescribed above and shown in FIG. 14, including vertical channels 122 a,vertical channels 122, circular outlet channel 125 and outlet 127.Housing outlet half 520 contains filter well 511, bounded by a planethat goes through filter seal surface 124 and by inner side wall 508.The upper part of the inner side wall contains a counter bore bounded byinner side wall 508 a and by surface 524. The bottom portion of ridge526 contains second inlet slot 502 a. Because housing outlet half 520does not contain an open chamber or plenum downstream of the BFFM, thehold up volume of biological fluid will be minimized.

Referring to FIG. 29, a biological fluid filtration media (BFFM) thatcontains at least one filter element is interposed between inlet 505 andoutlet 127, and is sealed to the housing to prevent the flow ofunfiltered biological fluid from flowing between the housing and theBFFM to prevent bypass of unfiltered biological fluid around the BFFM.The BFFM shown in FIG. 29 contains filter elements 15, 16, 17, and 18.The filter elements may all be of the same type or may be differenttypes filter elements. Each filter element contains an upstream surfacedesignated as upstream surface 15 a for filter element 15, a downstreamsurface designated as downstream surface 15 c for filter element 15, anda perimeter surface designated as perimeter surface 15 b for filterelement 15. The downstream surface of the BFFM shown as downstreamsurface 18 c of filter element 18 is in contact with inner wall 121 ofhousing outlet half 520. Because the downstream surface of the BFFMcontacts inner wall 121 of housing outlet half 520, BFFD 600 does notcontain an open chamber or plenum downstream of the BFFM. The air orliquid that is forced through the BFFM must pass through the verticalchannels and the circular outlet channel before flowing into outlet 127of BFFD 600. The at least one filter element may be sealed to thehousing with an interference fit between the perimeter surface of thefilter element and inner side wall 508 of housing outlet half 520, orthe at least one filter element may be sealed to the housing with acompression seal by compressing the outer periphery of the at least onefilter element between seal ring 550 and filter seal surface 124 ofhousing outlet half 520. Seal ring 550 is press fitted or bonded intothe counter bore at the top of filter well 511 as shown in FIG. 29. Theat least one filter element may also be sealed to the housing a heatseal, an ultrasonic weld, a glue seal, a solvent seal, a radio frequencyweld, or any other type of leak tight seal. A combination of sealingmethods may also be used to seal the at least one filter element to thehousing.

Referring to FIG. 29 a first fluid flow path is defined between inlet505 of BFFD 600 and outlet 127 of BFFD 600 with the at least one filterelement of the BFFM interposed between inlet 505 and outlet 127, andacross the fluid flow path. The first fluid flow path flows from inlet505, through first inlet slot 502, through second inlet slot 502 a, intoupstream chamber 513, through the at least one filter element of theBFFM, into vertical channels 122 and 122 a, into circular outlet channel125, and then into outlet 127.

Referring to FIG. 12 and FIG. 29, when BFFD 600 is used to replace BFFD200 in biological fluid filtration system 2000, the system will functionas follows. The user will purchase the system with all components asshown in FIG. 12, less feed blood bag 98. BFFD 600 will replace BFFD200, and tubing 85 and vent filtration device 40 will not be used. Theuser will connect tubing 81 to outlet 92 of feed blood bag 98 in amanner known in the art. Feed blood bag 98 and vent filtration device30, may be hung from a blood bag pole known in the art, and receivingblood bag 99 may be placed on a table top or the like. Tube clamp 95should be closed before connecting tubing 81 to feed blood bag 98.Before opening tube clamp 95 to start the flow of biological fluidthrough the system, tube clamp 96 should be open, and tube clamp 97should be closed.

Referring to FIG. 12, and FIG. 29, BFFD 600 functions as follows. Whentube clamp 95 is opened biological fluid (i.e. liquid) will flow fromfeed blood bag 98, through tubing 81, through inlet 505, through firstinlet slot 502, through second inlet slot 502 a and then into upstreamchamber 513 of BFFD 600. Upstream chamber 513 will rapidly fill withbiological fluid from the bottom up. The BFFM will wet and air will bepurged from BFFD 600 as described for the third embodiment above,because BFFD 600 uses the same filter under drain structure that wasused in BFFD 300 of the third embodiment.

Referring to FIG. 12, FIG. 29 and FIG. 31, once all of the air has beenpurged from within BFFD 600, biological fluid will continue to flowthrough the first fluid flow path from the inlet of BFFD 600 to theoutlet of BFFD 600, and then through tubing 82 into receiving blood bag99 until feed blood bag 98 is emptied of biological fluid. At this pointfeed blood bag 98 will be collapsed, effectively sealing the top oftubing 81, thereby preventing the flow of biological fluid in tubing 81.If receiving blood bag 99 is positioned at a level that is sufficientlylower than the outlet of BFFD 600, pressure downstream of the BFFM andupstream of outlet 127 will be negative as described above. Once feedblood bag 98 collapses and biological fluid flow through the first fluidflow path stops the differential pressure across the BFFM will becomezero, hence the pressure in upstream chamber 513 will become negative.The pressure on upstream surface 566 of flexible diaphragm 560 will beatmospheric because hole 571 of housing inlet half 501 is open toatmosphere, and in fluid flow communication with radial vent channel 503a and circular vent channels 503 of housing inlet half 501. Withatmospheric pressure on the outer surface 566 of flexible diaphragm 560,the negative pressure within upstream chamber 513 will cause flexiblediaphragm 560 to collapse onto upstream surface 15 a of the BFFM asshown in FIG. 32, thereby forcing the biological fluid in upstreamchamber 513 through the BFFM, into the vertical channels and thecircular outlet channel, into outlet 127, into tubing 82, and then intoreceiving blood bag 99.

Referring to FIG. 12, FIG. 29, and FIG. 30, when the filtration cycle iscomplete as just described, the BFFM will remain wetted, verticalchannels 122, vertical channels 122 a and circular outlet channel 125will be filled with biological fluid, and tubing 82 will be filled withbiological fluid. Because BFFD 600 does not contain a plenum downstreamof the BFFM, the hold up volume of biological fluid within BFFD 600 willbe minimized. The user will close tube clamp 96, and then cut and sealtubing 82 above tube clamp 96, and then discard BFFD 600 and feed bloodbag 98 in a safe manner. Tube clamp 97 may now be opened, and the air inreceiving blood bag 99 may be purged from receiving blood bag 99 bysqueezing receiving blood bag 99 thereby forcing the air in receivingblood bag 99 through the third fluid flow path from vent port 91 ofreceiving blood bag 99 to atmosphere. Tubing 84 can then be sealed andcut near receiving blood bag 99, and then tubing 84 and vent filtrationdevice 30 may be discarded in a safe manner.

BFFD 600 can be used to replace BFFD 100 in biological fluid filtrationsystem 1000 shown in FIG. 1. If BFFD 600 is used in this manner, it willpurge air and filter biological fluid as described in the thirdembodiment. Three tube connector 50 and vent filtration device 30 willfunction as described in the description of the first embodiment above.When the filtration cycle is complete, tubing 83, tubing 81 a, andupstream chamber 513 of BFFD 600 will drain as described in thedescription of the first embodiment above, and flexible diaphragm 560will remain in the un-collapsed state.

Detailed Description of the Seventh Embodiment

A seventh embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 33 through FIG.35. BFFD 700 contains a rigid housing that includes housing inlet half601 and housing outlet half 620. Housing seal surface 629 a of housinginlet half 601 is bonded to housing seal surface 629 of housing outlethalf 620. The bond is preferably an ultrasonic weld but may be a heatbond, a glue bond, a solvent bond, or any other type of leak tight bond.

Referring to FIG. 33, and FIG. 34 housing inlet half 601 containsdiaphragm well 609 bounded by surface 610 and a plane that goes throughthe top surface of ribs 604. Hole 671 goes through wall 612 and is influid flow communication with circular vent channels 603 and radial ventchannel 603 a. Vent filter element 670 may be sealed to surface 610 a sothat hole 671 is located within the seal as shown in FIG. 33. Ventfilter element 670 is preferably a sterilizing grade filter that may beeither hydrophobic, or hydrophilic. Vent filter element 670 adds aredundant layer of protection to BFFD 700. Flexible diaphragm 660contains inner surface 663, outer surface 666, and flange 662. The outersurface of flange 662 is sealed to diaphragm seal surface 607 of housinginlet half 601. The seal may be a heat seal, an ultrasonic seal, a glueseal, a solvent seal, or any other type of leak tight seal. Flexiblediaphragm 660 may be molded from a flexible rubber material such assilicone rubber, or it may be molded or thermo formed from a materialsuch as PVC, polyethylene, or polypropylene, but is not limited to thesematerials. Housing inlet half 601 also contains inlet 605, inlet slot602, and inlet tube socket 606. Upstream chamber 613 is bounded by innersurface 663 of flexible diaphragm 660, and by upstream surface 15 a offilter element 15, and by the inner surface of seal ring 650. Inlet 605is in fluid flow communication with upstream chamber 613 through inletslot 602. Inlet slot 602 is located at the bottom of upstream chamber613 and on the vertical center line of housing inlet half 601. Thebottom portion of diaphragm well 609 protrudes inward towards the centerof the diaphragm well so that inlet slot 602 is located outside ofdiaphragm seal surface 607 as shown in FIG. 34. Flexible diaphragm 660is preferably shaped so that in its normal state outer surface 666conforms to surface 610 of housing inlet half 601 as shown in FIG. 34and FIG. 35.

Referring to FIG. 33 housing outlet half 620 contains the same filterunder drain structure that was used in the first embodiment, and shownin FIG. 3, including vertical channels 22, horizontal channels 23,horizontal collection channel 26, outlet channel 25 and outlet 27.Housing outlet half 520 contains filter well 611 bounded by filter sealsurface 24 and by inner side wall 608. The upper part of the inner sidewall contains a counter bore bounded by inner side wall 608 a and bysurface 624.

Referring to FIG. 33, a biological fluid filtration media (BFFM) thatcontains at least one filter element is interposed between inlet 605 andoutlet 27, and is sealed to the housing to prevent the flow ofunfiltered biological fluid from flowing between the housing and theBFFM to prevent bypass of unfiltered biological fluid around the BFFM.The BFFM shown in FIG. 33 contains filter elements 15, 16, 17, and 18.The filter elements may all be of the same type or may be differenttypes filter elements. Each filter element contains an upstream surfacedesignated as upstream surface 15 a for filter element 15, a downstreamsurface designated as downstream surface 15 c for filter element 15, anda perimeter surface designated as perimeter surface 15 b for filterelement 15. The downstream surface of the BFFM shown as downstreamsurface 18 c of filter element 18 is in contact with inner wall 21 ofhousing outlet half 620. Because the downstream surface of the BFFMcontacts inner wall 21 of housing outlet half 620, BFFD 700 does notcontain an open chamber or plenum downstream of the BFFM. The air orliquid that is forced through the BFFM must pass through the verticalchannels 22, horizontal channels 23, horizontal collection channel 26,and outlet channel 25 before flowing into outlet 27 of BFFD 700. The atleast one filter element may be sealed to the housing with aninterference fit between the perimeter surface of the filter element andinner side wall 608 of housing outlet half 620, or the at least onefilter element may be sealed to the housing with a compression seal bycompressing the outer periphery of the at least one filter elementbetween seal ring 650 and filter seal surface 24 of housing outlet half620. Seal ring 650 is in the form of a hollow cylinder as shown in FIG.33. Seal ring 650 is press fitted or bonded into the counter bore at thetop of the filter well as shown in FIG. 33. The at least one filterelement may also be sealed to the housing a heat seal, an ultrasonicweld, a glue seal, a solvent seal, a radio frequency weld, or any othertype of leak tight seal. A combination of sealing methods may also beused to seal the at least one filter element to the housing.

Referring to FIG. 33 a first fluid flow path is defined between inlet605 of BFFD 700 and outlet 27 of BFFD 700 with the at least one filterelement of the BFFM interposed between inlet 605 and outlet 27, andacross the fluid flow path. The first fluid flow path flows from inlet605, through inlet slot 602, into upstream chamber 613, through the atleast one filter element of the BFFM, into vertical channels 22,horizontal channels 23, horizontal collection channel 26, outlet channel25, into outlet 27.

Referring to FIG. 12 and FIG. 33, when BFFD 700 is used to replace BFFD200 in biological fluid filtration system 2000, the system will functionas follows. The user will purchase the system with all components asshown in FIG. 12, less feed blood bag 98. BFFD 700 will replace BFFD200, and tubing 85 and vent filtration device 40 will not be used. Theuser will connect tubing 81 to outlet 92 of feed blood bag 98 in amanner known in the art. Feed blood bag 98 and vent filtration device30, may be hung from a blood bag pole known in the art, and receivingblood bag 99 may be placed on a table top or the like. Tube clamp 95should be closed before connecting tubing 81 to feed blood bag 98.Before opening tube clamp 95 to start the flow of biological fluidthrough the system, tube clamp 96 should be open, and tube clamp 97should be closed.

Referring to FIG. 12, and FIG. 33, BFFD 700 functions as follows. Whentube clamp 95 is opened biological fluid (i.e. liquid) will flow fromfeed blood bag 98, through tubing 81, through inlet 605, through inletslot 602, into upstream chamber 613 of BFFD 700. Upstream chamber 613will rapidly fill with biological fluid from the bottom up. The BFFMwill wet and air will be purged from BFFD 700 as described for the firstembodiment above, because BFFD 700 uses the same filter under drainstructure that was used in BFFD 100 of the first embodiment shown inFIG. 2 through FIG. 4.

Referring to FIG. 12, and FIG. 33, once all of the air has been purgedfrom within BFFD 700, biological fluid will continue to flow through thefirst fluid flow path from the inlet of BFFD 700 to the outlet of BFFD700, and then through tubing 82 into receiving blood bag 99 until feedblood bag 98 is emptied of biological fluid. At this point feed bloodbag 98 will be collapsed, effectively sealing the top of tubing 81,thereby preventing the flow of biological fluid in tubing 81. Ifreceiving blood bag 99 is positioned at a level that is sufficientlylower than BFFD 700, the pressure downstream of the BFFM and upstream ofoutlet 27 will be negative as described above in the first embodiment.Once feed blood bag 98 collapses and biological fluid flow through thefirst fluid flow path stops the differential pressure across the BFFMwill become zero, hence the pressure in upstream chamber 613 will becomenegative. The pressure on upstream surface 666 of flexible diaphragm 660will be atmospheric because hole 671 of housing inlet half 601 is influid flow communication to atmosphere via vent filter element 670, andin fluid flow communication with radial vent channel 603 a and circularvent channels 603 of housing inlet half 601. With atmospheric pressureon the outer surface 666 of flexible diaphragm 660, the negativepressure within upstream chamber 613 will cause flexible diaphragm 660to collapse onto upstream surface 15 a of the BFFM, thereby forcing thebiological fluid in upstream chamber 613 through the BFFM, into verticalchannels 22, horizontal channels 23, horizontal collection channel 26,outlet channel 25, into outlet 27, into tubing 82, and then intoreceiving blood bag 99.

Referring to FIG. 12, and FIG. 33, when the filtration cycle is completeas just described, the BFFM will remain wetted, vertical channels 22,horizontal channels 23, horizontal collection channel 26, and outletchannel 25, will be filled with biological fluid, and tubing 82 will befilled with biological fluid. Because BFFD 700 does not contain a plenumdownstream of the BFFM, the hold up volume of biological fluid withinBFFD 700 will be minimized. The user will close tube clamp 96, and thencut and seal tubing 82 above tube clamp 96, and then discard BFFD 700and feed blood bag 98 in a safe manner. Tube clamp 97 may now be opened,and the air in receiving blood bag 99 may be purged from receiving bloodbag 99 by squeezing receiving blood bag 99 thereby forcing the air inreceiving blood bag 99 through the third fluid flow path from vent port91 of receiving blood bag 99 to atmosphere. Tubing 84 can then be sealedand cut near receiving blood bag 99, and then tubing 84 and ventfiltration device 30 may be discarded in a safe manner.

BFFD 700 can be used to replace BFFD 100 in biological fluid filtrationsystem 1000 shown in FIG. 1. If BFFD 700 is used in this manner, it willpurge air and filter biological fluid as described in the firstembodiment. Three tube connector 50 and vent filtration device 30 willfunction as described in the description of the first embodiment above.When the filtration cycle is complete, tubing 83, tubing 81 a, andupstream chamber 613 of BFFD 700 will drain as described in thedescription of the first embodiment above, and flexible diaphragm 660will remain in the un-collapsed state.

Detailed Description of the Eighth Embodiment

An eighth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 36 through FIG.39. BFFD 800 contains a rigid housing that includes housing inlet half701 and housing outlet half 720. Housing seal surface 729 a of housinginlet half 701 is bonded to housing seal surface 729 of housing outlethalf 720. The bond is preferably an ultrasonic weld but may be a heatbond, a glue bond, a solvent bond, or any other type of leak tight bond.Housing inlet half 701 is the same as housing inlet half 1 of the firstembodiment except that inlet slot 702 is located at the bottom ofupstream chamber 713, and housing inlet half 701 does not contain afilter well. The inlet slot 702 could instead be located anywhere abovethe bottom of upstream chamber 713. Housing outlet half 720 is the sameas housing outlet half 20 of the first embodiment, except that housingoutlet half 720 contains a first filter well 711 bounded by inner sidewall 708 and a plane that goes through first filter seal surface 724,and second filter well 711 a bounded by inner side wall 708 a and secondfilter seal surface 724 a. First filter well 711 has a larger diameterthan second filter well 711 a. The first filter well is concentric withthe second filter well.

Referring to FIG. 36 through FIG. 39, the BFFM contains four filterelements, first filter element 715, second filter element 716, thirdfilter element 717, and fourth filter element 718 comprised of threelayers of filter material of the same type. Any of the filter elementsmay contain one or more layers of the filter material of the same type.The first filter element has a pore size greater than the pore size ofthe second filter element, the fourth filter element has a pore sizesmaller than the pore size of the second filter element, while the thirdfilter element has a pore size greater than the pore size of the secondfilter element. Preferably the pore size of the third filter element isgreater than the pore size of the first and second filter elements. WhenBFFD 800 is used to filter blood or blood product, first filter element715 may be sized to remove gels from the blood or blood product, secondfilter element 716 may be sized to remove microaggregates from the bloodor blood product, fourth filter element 718 may be sized to removeleukocytes from the blood or blood product, while the third filterelement 717 is sized to act as a flow distribution layer. Because gelsand microaggregates are large particles they may clump together therebyreducing the flow through the gel-microaggregate filter elements in theregion of the clump. The flow distribution filter element willdistribute the effluent from the microaggregate filter element evenlyover the upstream surface of the leukocyte removing layer, therebyallowing the leukocyte removing layer to be utilized most efficiently.The outside diameter of first filter element 715 is smaller than theinside diameter of inner side wall 708 of housing outlet half 720 (shownby gap 770 in FIG. 37) preventing first filter element 715 from beingsealed to BFFD 800 with an interference fit between the perimetersurface 715 b of filter element 715 and inner side wall 708 of housingoutlet half 720. First filter element 715 is sealed to the housing bycompressing the outer periphery of filter element 715 between filterseal surface 707 of housing inlet half 701, and first filter sealsurface 724 of housing outlet half 720 as shown in FIG. 36 and FIG. 37.Second filter element 716 and fourth filter element 718 are sealed tothe housing an interference fit between the perimeter surface of eachfilter element and inner side wall 708 a of housing outlet half 720.Third filter element 717 is preferably a woven or non-woven screenfilter, but could be any type of open pore size depth filter. The mainpurpose of filter element 717 is flow distribution, therefore it has alarge pore size, and is preferably structured to allow flow through itin all directions. Hence the perimeter surface of filter element 717need not have an interference fit with inner side wall 708. Inapplications where the blood or blood product is fresh and does notcontain gels, the first filter element may be a microaggregate removingfilter element, and the second filter element could be eliminated. Inthis case the third filter element may also be eliminated. As shown inFIG. 36 through FIG. 38, first filter well 711 has a larger insidediameter than second filter well 711 a, therefore the filter elementsdisposed in the first filter well will have a larger outside diameterthan the filter elements disposed in the second filter well. Alternatelya single filter well as shown in FIG. 13 could be used. Referring toFIG. 13, filter element 15 could be a gel removing filter element,filter element 16 could be a microaggregate removing filter element,filter element 17 could be a flow distribution filter element, andfilter element 18 could be a leukocyte removing filter element. As shownin FIG. 13 first filter element 15 has an outside diameter smaller thanthe inside diameter of the inner side wall of the housing outlet half.Alternately, first filter element 15 could have an outside diameterlarge enough to seal it to the housing with an interference fit betweenits outer perimeter and the inner side wall of the housing outlet half,and either the second filter element, or the fourth filter element couldhave an outside diameter smaller than the inside diameter of the innerside wall of the housing outlet half.

The housing of BFFD 800 is the same as the housing of BFFD 100 of thefirst embodiment described above with the minor modifications notedabove. Therefore BFFD 800 will function exactly as BFFD 100 when used inbiological fluid filtration system 1000 of the first embodiment shown inFIG. 1.

If the vent inlet, vent inlet slot, and vent tube socket (shown in FIG.13) are added to housing inlet half 701, BFFD 800 could be used inbiological fluid filtration system 2000 shown in FIG. 12. In this caseBFFD 800 would fill and purge air from within BFFD 800 as described inthe first embodiment. After the air was purged from BFFD 800, it wouldfunction the same as BFFD 200 in biological fluid filtration system2000.

Housing outlet half 720 could use the filter under drain structure ofthe second embodiment shown in FIG. 14, in place of the filter underdrain structure of the first embodiment. In this case BFFD 800 wouldfill and purge air from within BFFD 800 as described in the secondembodiment.

Detailed Description of the Ninth Embodiment

A ninth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 40, FIG. 43, andFIG. 44. BFFD 900 may be used in place of BFFD 100 in biological fluidfiltration system 1000 shown in FIG. 1, and may also be used in place ofBFFD 200 in biological fluid filtration system 2000 shown in FIG. 12.

Referring to FIG. 40, and FIG. 43, BFFD 900 contains a rigid housingthat includes housing inlet half 801 and housing outlet half 820.Housing seal surface 829 a of housing inlet half 801 is bonded tohousing seal surface 829 of housing outlet half 820. The bond ispreferably an ultrasonic weld but may be a heat bond, a glue bond, asolvent bond, or any other type of leak tight bond.

Referring to FIG. 40, housing inlet half 801 contains a diaphragm wellsimilar to diaphragm well 509 of housing inlet half 501 shown in FIG.31. Hole 871 goes through wall 812 and is in fluid flow communicationwith circular vent channels 803 and radial vent channel 803 a. Thecircular vent channels and the radial vent channel are similar to thecircular vent channels and the radial vent channel of housing inlet half501 shown in FIG. 31. Flexible diaphragm 860 contains inner surface 863,outer surface 866, and flange 862. Flexible diaphragm 860 is similar toflexible diaphragm 560 shown in FIG. 29. The outer surface of flange 862is sealed to diaphragm seal surface 807 of housing inlet half 801. Theseal may be a heat seal, an ultrasonic seal, a glue seal, a solventseal, or any other type of leak tight seal. Flexible diaphragm 860 maybe molded from a flexible rubber material such as silicone rubber, or itmay be molded or thermo formed from a material such as PVC,polyethylene, or polypropylene, but is not limited to these materials.Flexible diaphragm 860 is preferably shaped so that in its normal stateouter surface 866 conforms to surface 810 of housing inlet half 801.Upstream chamber 813 is bounded by inner surface 863 of flexiblediaphragm 860, and by surface 808 b of housing outlet half 820, and byupstream surface 815 a of filter element 815, and by the inner surfaceof seal ring 850.

Referring to FIG. 40, FIG. 43, and FIG. 44 housing outlet half 820contains an open chamber or plenum 830 defined by inner wall 821 a, byinner side wall 808 b, and by a plane that goes through second filterseal surface 824 a. Vertical filter support ribs 822 protrude from innerwall 821 a, with the top surface of vertical filter support ribs lyingin a plane that goes through second filter seal surface 824 a. Plenum830 may be tapered as shown in FIG. 40, with the depth of the top of theplenum being deeper than the depth of the bottom of the plenum. Outlet827 is located at the top of plenum 830. Vertical filter support ribs822 create a filter under drain structure. Housing outlet half 820contains first filter well 811 bounded by inner side wall 808 and byfirst filter seal surface 824, and second filter well 811 a bounded byinner side wall 808 a and by second filter seal surface 824 a. Firstfilter well 811 has a larger diameter than second filter well 811 a. Thehorizontal center line of the first filter well is offset below thehorizontal center line of the second filter well so that the top offirst filter seal surface 824 protrudes above the top of second filterseal surface 824 a a sufficient distance to create a compression seal aswill be described below, and so that the perimeter of the second filterwell is located entirely within the perimeter of the first filter well.Housing outlet half 820 also contains inlet 805, inlet slot 802,circular groove 888, and slot 804. Inlet 805 is in fluid flowcommunication with upstream chamber 813 via inlet slot 802, circulargroove 888, and slot 804. The upper part of first filter well 811contains a seal ring counter bore bounded by inner side wall 808 b, andby surface 824 b.

Referring to FIG. 40, FIG. 43, and FIG. 44, the BFFM contains six filterelements, first filter element 815, second filter element 816, thirdfilter element 817, fourth filter element 818 comprised of three layersof filter material of the same type, fifth filter element 877, and sixthfilter element 814. Any of the filter elements may contain one or morelayers of the filter material of the same type. The first filter elementhas a pore size greater than the pore size of the second filter element,the fourth filter element has a pore size smaller than the pore size ofthe second filter element, while the third filter element has a poresize greater than the pore size of the second filter element. Preferablythe pore size of the third filter element is greater than the pore sizeof the first and second filter elements. The fifth filter element has apore size greater than the fourth filter element, and the sixth filterelement has a pore size smaller than the fifth filter element. When BFFD900 is used to filter blood or blood product, first filter element 815may be sized to remove gels from the blood or blood product, secondfilter element 816 may be sized to remove microaggregates from the bloodor blood product, fourth filter element 818 may be sized to removeleukocytes from the blood or blood product, while the third filterelement 817 is sized to act as a first flow distribution layer. Sixthfilter element 814 is used to remove particulates from the filterelements upstream of it, while fifth filter element 877 acts as a secondflow distribution layer. Because gels and microaggregates are largeparticles they may clump together thereby reducing the flow through thegel-microaggregate filter elements in the region of the clump. The firstflow distribution filter element will distribute the effluent from themicroaggregate filter element evenly over the upstream surface of theleukocyte removing layer, thereby allowing the leukocyte removing layerto be utilized most efficiently. Once the gels and microaggregates havebeen removed from the blood or blood product, the blood or blood productwill be relatively clean and therefore the surface area of the leukocyteremoving layer may be made smaller than the surface area of the gel andmicroaggregate layers, thereby reducing the hold up volume of the BFFD.The gel filter element, and the microaggregate filter element, and thefirst flow distribution filter element, are inserted into the firstfilter well of housing outlet half 820. Referring to FIG. 40 and FIG.44, gel filter element 815, microaggregate filter element 816, and firstflow distribution filter element 817, have outside diameters smallerthan the inside diameter of inner side wall 808, preventing them frombeing sealed to BFFD 900 with an interference fit between the perimetersurface of each respective filter element and inner side wall 808 ofhousing outlet half 820. The outer periphery of the gel filter element,and the outer periphery of the microaggregate filter element, and theouter periphery of the first flow distribution filter element, aresealed to the housing with a compression seal between seal ring 850, andfirst filter seal surface 824 of housing outlet half 820 as shown inFIG. 40. Seal ring 850 is in the shape of a hollow cylinder with atapered inner surface as shown in FIG. 40. Alternately, either the gelfilter element, or the microaggregate filter element, could have anoutside diameter large enough so that it could be sealed to the housingan interference fit between the perimeter surface of the larger diameterfilter element and inner side wall 808 of housing outlet half 820. Thirdfilter element 817 is preferably a woven or non-woven screen filter, butcould be any type of open pore size depth filter, or could even be aninjection molded screen. The main purpose of first flow distributionfilter element 817 is flow distribution, therefore it has a large poresize (i.e. the pore size of flow distribution filter element 817 may belarger than the pore size of all of the other filter elements), and ispreferably structured to allow flow through it in all directions (i.e.through the flow distribution filter element, and laterally across theflow distribution filter element in both the horizontal and verticaldirections). Hence the perimeter surface of filter element 817 need nothave an interference fit with inner side wall 808. Housing outlet half820 also contains a second filter well smaller in diameter than thefirst filter well into which leukocyte removing filter element 818,second flow distribution filter element 877, and particle trappingfilter element 814, are inserted. Leukocyte removing filter element 818is sealed to the housing an interference fit between the perimetersurface of each layer of the leukocyte removing filter material andinner side wall 808 a of housing outlet half 820. As shown in FIG. 40,second flow distribution filter element 877 and particle removing filterelement 814 have outside diameters smaller than the inside diameter ofinner side wall 808 a, thereby preventing an interference seal betweenthe perimeter surface of each respective filter element and inner sidewall 808 a of housing outlet half 820. The main purpose of second flowdistribution filter element 877 is flow distribution, therefore it has alarge pore size, and is preferably structured to allow flow through itin all directions. Hence the perimeter surface of filter element 877need not have an interference fit with inner side wall 808 a. As shownin FIG. 40, the outer periphery of the downstream surface of particletrapping filter element 814 is sealed to second filter seal surface 824a of housing outlet half 820 with a compression seal. Alternately eitherfilter element 877 or filter element 814, or both could have asufficiently large outside diameter so that they could be sealed to thehousing an interference fit between the perimeter surface of eachrespective filter element and inner side wall 808 a of housing outlethalf 820. Particle trapping filter element 814 could also be sealed tohousing outlet half 820 by a heat seal, an ultrasonic seal, a solventseal, a glue seal, or any other type of leak tight seal. In someapplications second flow distribution filter element 877 could beeliminated.

Referring to FIG. 40 and FIG. 43, a first fluid flow path is definedbetween inlet 805 of BFFD 900 and outlet 827 of BFFD 900 with the BFFMinterposed between inlet 805 and outlet 827, and across the fluid flowpath. The first fluid flow path flows from inlet 805, through inlet slot802, through circular groove 888 in both directions (as shown by arrows885 in FIG. 43), through slot 804, into upstream chamber 813, throughthe BFFM, into the plenum 830 downstream of the BFFM, and then intooutlet 827.

Referring to FIG. 12 and FIG. 40, when BFFD 900 is used to replace BFFD200 in biological fluid filtration system 2000, the system will functionas follows. The user will purchase the system with all components asshown in FIG. 12, less feed blood bag 98. BFFD 900 will replace BFFD200, tubing 85 and vent filtration device 40 will not be used. The userwill connect tubing 81 to outlet 92 of feed blood bag 98 in a mannerknown in the art. Feed blood bag 98 and vent filtration device 30, maybe hung from a blood bag pole known in the art, and receiving blood bag99 may be placed on a table top or the like. Tube clamp 95 should beclosed before connecting tubing 81 to feed blood bag 98. Before openingtube clamp 95 to start the flow of biological fluid through the system,tube clamp 96 should be open, and tube clamp 97 should be closed.

Referring to FIG. 12, FIG. 40, and FIG. 43, BFFD 900 functions asfollows. When tube clamp 95 is opened biological fluid (i.e. liquid)will flow from feed blood bag 98, through tubing 81, into inlet 805,through inlet slot 802, through circular groove 888 in both directions(as shown by arrows 885 in FIG. 43), through slot 804, into upstreamchamber 813. Upstream chamber 813 will rapidly fill with biologicalfluid from the bottom up. As upstream chamber 813 fills from the bottomup, the initial air in upstream chamber 813 will be displaced by thebiological fluid filling upstream chamber 813. The displaced air will beforced through the BFFM, into plenum 830, and then into outlet 827. Thebiological fluid in upstream chamber 813 will be pressurized, with thepressure at the bottom of upstream chamber 813 being proportional to thedistance from the top of the biological fluid in feed blood bag 98 tothe bottom of upstream chamber 813, and with the pressure at the top ofupstream chamber 813 being proportional to the distance from the top ofthe biological fluid in feed blood bag 98 to the top of upstream chamber813. Hence the pressure at the top of upstream chamber 813 will be lessthan the pressure at the bottom of upstream chamber 813. The positivepressure in upstream chamber 813 will cause the biological fluid to flowthrough first filter element 815, and second filter element 816 over theentire surface area of the first and second filter elements displacingthe air within the pores of the first and second filter elements withbiological fluid, thereby wetting the first and second filter elementsfrom the upstream side of first filter element 815 to the downstreamside of second filter element 816. The displaced air from upstreamchamber 813 and from the first and second filter elements will flow intothird filter element 817. Third filter element 817 preferably has anopen pore size with a structure that allows flow through it in alldirections. Therefore any air or biological fluid that flows from thedownstream surface of second filter element 816, will flow into thirdfilter element 817 and then be uniformly distributed over the entireupstream surface of fourth filter element 818, thereby utilizing fourthfilter element 818 in the most efficient way. As the first and secondfilter elements wet, the air that was initially in the pores of thefirst and second filter elements will be displaced by biological fluid,and flow into the third filter element 817. Because the pressure at thebottom of upstream chamber 813 is greater than the pressure at the topof upstream chamber 813, the flow rate of biological fluid through thefirst and second filter elements will be greater at the bottom of thefirst and second filter elements than at the top of the first and secondfilter elements. Therefore, the first and second filter elements willfirst become completely wetted from the upstream surface of the firstfilter element to downstream surface of the second filter element at thebottom of the second filter element. The first and second filterelements will continue to wet with the downstream surface of the secondfilter element wetting from the bottom to the top. The third filterelement will also wet from the bottom to the top. When the liquid levelin the third filter element reaches the bottom of fourth filter element818, the fourth filter element will begin to wet from the bottom up. Thefirst and second filter elements will continue to wet until all of theair in the first and second filter elements has been purged. It isimportant that the horizontal center line of first filter well 811 isoffset the required distance below the horizontal center line of secondfilter well 811 a so that the top of first filter seal surface 824protrudes above the top of second filter seal surface 824 a no more thanthe distance required to create a compression seal at the top of thefirst filter well between seal ring 850 and first filter seal surface824 of housing outlet half 820, because air will be trapped in thecompression seal portion of the first, second, and third filter elementsthat lie above horizontal line 886 shown in FIG. 43. The fourth, fifth,and sixth filter elements will wet from the bottom up, with thedownstream surface of the sixth filter element also wetting from thebottom up, because the pressure at the bottom of the upstream surface ofthe fourth filter element will be greater than the pressure at the topof the upstream surface of the fourth filter element. Once the bottom ofthe downstream surface of the sixth filter element has been wetted, theremainder of the downstream surface of the sixth filter element willcontinue to wet from the bottom up, and biological fluid will start toflow from the bottom of the sixth filter element, into plenum 830. Theplenum will fill from the bottom up forcing the air above the liquidlevel in the plenum into outlet 827, into tubing 82, and then intoreceiving blood bag 99. The plenum will fill with biological fluidbefore all of the air has been purged from the upper portion of thefourth, fifth, and sixth filter elements. The remaining air in the upperportion of the fourth, fifth, and sixth filter elements will bedisplaced by biological fluid and forced into the plenum, where it willbubble to the top of the plenum due to the buoyancy of air in thebiological fluid, and then be forced into outlet 827, into tubing 82,and then into receiving blood bag 99 by the flow of biological fluidfrom plenum 830 into outlet 827. Hence the initial flow of biologicalfluid through outlet 827, into tubing 82 will be a mixture of air andbiological fluid, so that the initial flow into tubing 82 will consistof alternate segments of biological fluid and air.

Referring to FIG. 12, and FIG. 40, once all of the air has been purgedfrom within BFFD 900, biological fluid will continue to flow through thefirst fluid flow path from the inlet of BFFD 900 to the outlet of BFFD900, and then through tubing 82 into receiving blood bag 99 until feedblood bag 98 is emptied of biological fluid. At this point feed bloodbag 98 will be collapsed, effectively sealing the top of tubing 81,thereby preventing the flow of biological fluid in tubing 81. Ifreceiving blood bag 99 is positioned at a level that is sufficientlylower than BFFD 900, pressure P3 downstream of the BFFM and upstream ofoutlet 827 will be negative as described above. Once feed blood bag 98collapses and biological fluid flow through the first fluid flow pathstops the differential pressure across the BFFM will become zero, hencethe pressure in upstream chamber 813 will become negative. The pressureon upstream surface 866 of flexible diaphragm 860 will be atmosphericbecause hole 871 of housing inlet half 801 is open to atmosphere, andhole 871 is in fluid flow communication with radial vent channel 803 a,and circular vent channels 803. With atmospheric pressure on the outersurface 866 of flexible diaphragm 860, the negative pressure withinupstream chamber 813 will cause flexible diaphragm 860 to collapse ontothe upstream surface of first filter element 815, thereby forcing thebiological fluid in upstream chamber 813 through the BFFM, into plenum830, into outlet 827, into tubing 82, and then into receiving blood bag99.

Referring to FIG. 12 and FIG. 40, when the filtration cycle is completeas just described, the BFFM will remain wetted, plenum 830 will befilled with biological fluid, and tubing 82 will be filled withbiological fluid. The user will close tube clamp 96, and then cut andseal tubing 82 above tube clamp 96, and then discard BFFD 900 and feedblood bag 98 in a safe manner. Tube clamp 97 may now be opened, and theair in receiving blood bag 99 may be purged from receiving blood bag 99by squeezing receiving blood bag 99 thereby forcing the air in receivingblood bag 99 through the third fluid flow path from vent port 91 ofreceiving blood bag 99 to atmosphere. Tubing 84 can then be sealed andcut near receiving blood bag 99, and then tubing 84 and vent filtrationdevice 30 may be discarded in a safe manner.

The filter under drain structure of BFFD 900 including plenum 830 andvertical filter support ribs 822 may be replaced with the filter underdrain structure of the first embodiment shown in FIG. 3, in which casethe filter under drain structure would purge air and fill withbiological fluid as described in the description of the firstembodiment. If the filter under drain structure of the first embodimentis used to replace plenum 830 and vertical filter support ribs 822, thehold up volume of the BFFD will also be minimized as explained in thedescription of the first embodiment, because of the lack of a plenum.

The filter under drain structure of BFFD 900 including plenum 830 andvertical filter support ribs 822 may also be replaced with the filterunder drain structure of the second embodiment shown in FIG. 14, inwhich case the filter under drain structure would purge air and fillwith biological fluid as described in the second embodiment. If thefilter under drain structure of the second embodiment is used to replaceplenum 830 and vertical filter support ribs 822, the amount of air thatwill be purged from the BFFM after biological fluid starts to flow fromthe outlet will be minimized, and the hold up volume of the BFFD willalso be minimized as explained in the description of the secondembodiment, because of the lack of a plenum.

FIG. 41 shows BFFD 900 without fifth filter element 877, and withoutsixth filter element 814. The first and second filter elements aresealed to the housing with an interference seal between the perimetersurface of the first and second filter elements and inner side wall 808of housing outlet half 820. The outer periphery of the first filterelement is also compression sealed by seal ring 850. The fourth filterelement has an outside diameter less than the inside diameter of innerside wall 808 a. The outer periphery of each layer of filter material ofthe fourth filter element is bonded to the layer adjacent to it withbond 876, with the outer periphery of the downstream surface of thefourth filter element sealed to second filter seal surface 824 a withbond 875. The bond could be a heat bond, an ultrasonic bond, a solventbond, a glue bond, an R.F. bond or any other type of leak tight seal.

FIG. 42 shows BFFD 900 with the outside diameter of the first and secondfilter elements less than the inside diameter of inner side wall 808.The outer periphery of the upstream surface of the first filter elementis compression sealed by seal ring 850. The outer periphery of thedownstream surface of the first filter element is bonded to the outerperiphery of the upstream surface of the second filter element with bond879; the outer periphery of the downstream surface of the second filterelement is bonded to the upstream surface of the outer periphery of thethird filter element; and the outer periphery of the third filterelement is bonded to first filter seal surface 824 with bond 878. Thebond could be a heat bond, an ultrasonic bond, a solvent bond, a gluebond, an R.F. bond or any other type of leak tight seal. The fourthfilter element is sealed to the housing with an interference sealbetween the perimeter surface of the fourth filter element and innerside wall 808 a of housing outlet half 820. The outside diameter of thefifth and sixth filter elements is less than the inside diameter ofinner side wall 808 a. The outer periphery of the downstream surface ofthe sixth filter element is bonded to second filter seal surface 824 awith bond 887. The bond could be a heat bond, an ultrasonic bond, asolvent bond, a glue bond, an R.F. bond or any other type of leak tightseal.

FIG. 45 shows BFFD 900 with the perimeter surface of the first, second,and third, filter elements bonded to inner side wall 808 of housingoutlet half 820 with bond 874, and with the perimeter surface of thefourth, fifth, and sixth, filter elements bonded to inner side wall 808a of housing outlet half 820 with bond 873. The bonds could be a heatbond, an ultrasonic bond, a solvent bond, a glue bond, an R.F. bond orany other type of leak tight seal.

The various filter elements could also be sealed to the housing anycombination of seals shown in FIG. 40 through FIG. 42, and FIG. 45.

Detailed Description of the Tenth Embodiment

A tenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 46 through FIG.48. BFFD 1000 contains a rigid housing that includes housing inlet half901 and housing outlet half 920. Housing seal surface 929 a of housinginlet half 901 is bonded to housing seal surface 929 of housing outlethalf 920. The bond is preferably an ultrasonic weld but may be a heatbond, a glue bond, a solvent bond, or any other type of leak tight bond.

Referring to FIG. 48 housing inlet half 901 contains circular rib 989,and filter support ribs 909. Slot 904 a extends through the side wall ofcircular rib 989. Filter seal surface 907 extends 360° around the top ofcircular rib 989.

Referring to FIG. 46 and FIG. 47 housing outlet half 920 contains anopen chamber or plenum 930 defined by inner wall 921 a, by inner sidewall 908 b, and by a plane that goes through second filter seal surface924 a. Vertical filter support ribs 922 protrude from inner wall 921 a,with the top surface of vertical filter support ribs lying in a planethat goes through second filter seal surface 924 a. Plenum 930 may betapered as shown in FIG. 46, with the depth of the top of the plenumbeing deeper than the depth of the bottom of the plenum. Outlet 927 islocated at the top of plenum 930. The vertical filter support ribscreate a filter under drain structure that is the same as the filterunderdrain structure used in the ninth embodiment. Housing outlet half920 contains first filter well 911 bounded by inner side wall 908 and byfirst filter seal surface 924, and second filter well 911 a bounded byinner side wall 908 a and by second filter seal surface 924 a. Firstfilter well 911 has a larger diameter than second filter well 911 a. Thefirst filter well is concentric with the second filter well. Housingoutlet half 920 also contains inlet 905, inlet slot 902, circular groove988, and slot 904. Inlet 905 is in fluid flow communication withupstream chamber 913 via inlet slot 902, circular groove 988, slot 904,and slot 904 a of housing inlet half 901.

Referring to FIG. 46, the BFFM contains six filter elements, firstfilter element 915, second filter element 916, third filter element 917,fourth filter element 918, fifth filter element 977, and sixth filterelement 914. Any of the filter elements may contain one or more layersof the filter material of the same type. The first filter element has apore size greater than the pore size of the second filter element, thefourth filter element has a pore size smaller than the pore size of thesecond filter element, while the pore size of the third filter elementhas a pore size greater than the pore size of the second filter element.Preferably the pore size of the third filter element is greater than thepore size of the first and second filter elements. The fifth filterelement has a pore size greater than the fourth filter element, and thesixth filter element has a pore size smaller than the fifth filterelement. When BFFD 1000 is used to filter blood or blood product, firstfilter element 915 may be sized to remove gels from the blood or bloodproduct, second filter element 916 may be sized to removemicroaggregates from the blood or blood product, fourth filter element918 may be sized to remove leukocytes from the blood or blood product,while the third filter element 917 is sized to act as a first flowdistribution layer. Sixth filter element 914 is used to removeparticulates from the filter elements upstream of it, while fifth filterelement 977 acts as a second flow distribution layer. Because gels andmicroaggregates are large particles they may clump together therebyreducing the flow through the gel-microaggregate filter elements in theregion of the clump. The first flow distribution filter element willdistribute the effluent from the microaggregate filter element evenlyover the upstream surface of the leukocyte removing layer, therebyallowing the leukocyte removing layer to be utilized most efficiently.The gel filter element, and the microaggregate filter element areinserted into the first filter well of housing outlet half 820. Gelfilter element 915 has outside diameters smaller than the insidediameter of inner side wall 908, preventing it from being sealed to BFFD1000 with an interference fit between its perimeter surface and innerside wall 908 of housing outlet half 920. The outer periphery of the gelfilter element, and the outer periphery of the microaggregate filterelement, are sealed to the housing with a compression seal betweenfilter seal surface 907 of housing inlet half 920, and first filter sealsurface 924 of housing outlet half 920. In addition the microaggregatefilter element has an interference fit between its perimeter surface andinner side wall 908 of housing outlet half 920. Alternately, the gelfilter element could have an outside diameter large enough so that itcould be sealed to the housing an interference fit between its perimetersurface and inner side wall 908 of housing outlet half 920, and themicroaggregate filter element could have an outside diameter smallerthan the inside diameter of inner side wall 908 of housing outlet half920, or both the gel filter element and the microaggregate filterelements could have an outside diameter smaller than the inside diameterof inner side wall 908 of housing outlet half 920. In applications wherethe blood or blood product does not contain gels, the gel filter elementcould be eliminated. Housing outlet half 920 also contains second filterwell 911 a that is smaller in diameter than the first filter well 911into which first flow distribution filter element 917, leukocyteremoving filter element 918, second flow distribution filter element977, and particle trapping filter element 914, are inserted. First flowdistribution filter element 917 is preferably a woven or non-wovenscreen filter, but could be any type of open pore size depth filter, orit could be a molded screen. The main purpose of first flow distributionfilter element 917 is flow distribution, therefore it has a large poresize, and is preferably structured to allow flow through it in alldirections. Hence the perimeter surface of third filter element 917 neednot have an interference fit with inner side wall 908 a of housingoutlet half 920. Leukocyte removing filter element 918 is sealed to thehousing an interference fit between the perimeter surface of theleukocyte removing filter element and inner side wall 908 a of housingoutlet half 920. Second flow distribution filter element 977 andparticle removing filter element 914 are also sealed to the housing aninterference seal between the perimeter surface of each respectivefilter element and inner side wall 908 a of housing outlet half 920. Themain purpose of second flow distribution filter element 977 is flowdistribution, therefore it has a large pore size, and is preferablystructured to allow flow through it in all directions. Hence it is notnecessary that the perimeter surface of filter element 977 have aninterference fit with inner side wall 908 a. In some applications thesecond flow distribution filter element may be eliminated. As shown inFIG. 46 and FIG. 47, first filter well 911 has a larger inside diameterthan second filter well 911 a, therefore the filter elements disposed inthe first filter well will have a larger outside diameter than thefilter elements disposed in the second filter well. Alternately a singlefilter well as shown in FIG. 13 could be used. Referring to FIG. 13,filter element 15 could be a gel removing filter element, filter element16 could be a microaggregate removing filter element, filter element 17could be a first flow distribution filter element, filter element 18could be a leukocyte removing filter element, and a second flowdistribution filter element could be added downstream of filter element18, with a particle removing filter element added downstream of thesecond flow distribution filter element. As shown in FIG. 13 firstfilter element 15 has an outside diameter smaller than the insidediameter of the inner side wall of the housing outlet half. Alternately,first filter element 15 could have an outside diameter large enough toseal it to the housing with an interference fit between its outerperimeter and the inner side wall of the housing outlet half, and eitherthe second filter element, or the fourth filter element could have anoutside diameter smaller than the inside diameter of the inner side wallof the housing outlet half, or the first and second filter elementscould have an outside diameter smaller than the inside diameter of theinner side wall of the housing outlet half.

Referring to FIG. 46, a first fluid flow path is defined between inlet905 of BFFD 1000 and outlet 927 of BFFD 1000 with the BFFM interposedbetween inlet 905 and outlet 927, and across the fluid flow path. Thefirst fluid flow path flows from inlet 905, through inlet slot 902, inboth directions through circular groove 988, through slot 904, throughslot 904 a, into upstream chamber 913, through the BFFM, into the plenum930 downstream of the BFFM, and then into outlet 927.

Referring to FIG. 1 and FIG. 46, when BFFD 1000 is used to replace BFFD100 in biological fluid filtration system 1000, the system will functionas follows. The user will purchase the system with all components asshown in FIG. 1, less feed blood bag 98. BFFD 1000 will replace BFFD100. The user will connect tubing 81 to outlet 92 of feed blood bag 98in a manner known in the art. Feed blood bag 98 and vent filtrationdevice 30, and vent filtration device 40, may be hung from a blood bagpole known in the art, and receiving blood bag 99 may be placed on atable top or the like. Tube clamp 95 should be closed before connectingtubing 81 to feed blood bag 98. Before opening tube clamp 95 to startthe flow of biological fluid through the system, tube clamp 96 should beopen, and tube clamp 97 should be closed.

Referring to FIG. 1 and FIG. 46, BFFD 1000 functions as follows. Whentube clamp 95 is opened biological fluid (i.e. liquid) will flow fromfeed blood bag 98. Three tube connector 50 and vent filtration device 30will function as described in the description of the first embodiment.Biological fluid will flow into inlet 905, through inlet slot 902,through circular groove 988 in both directions, through slot 904,through slot 904 a, into upstream chamber 913, of BFFD 1000. Upstreamchamber 913 will rapidly fill with biological fluid from the bottom up.As upstream chamber 913 fills from the bottom up, the initial air inupstream chamber 913 will be displaced by the biological fluid fillingupstream chamber 913. The displaced air will be forced through the BFFM,into plenum 930, and then into outlet 927 all of BFFD 1000. Thebiological fluid in upstream chamber 913 will be pressurized, with thepressure at the bottom of upstream chamber 913 being proportional to thedistance from the top of the biological fluid in feed blood bag 98 tothe bottom of upstream chamber 913, and with the pressure at the top ofupstream chamber 913 being proportional to the distance from the top ofthe biological fluid in feed blood bag 98 to the top of upstream chamber913. Hence the pressure at the top of upstream chamber 913 will be lessthan the pressure at the bottom of upstream chamber 913. The positivepressure in upstream chamber 913 will cause the biological fluid to flowthrough the BFFM over the entire surface area of the BFFM and todisplace the air within the pores of the BFFM with biological fluid,thereby wetting BFFM from the upstream side of first filter element 915of the BFFM to the downstream side of sixth filter element 914 of theBFFM. As the BFFM wets the air that was initially in the pores of BFFMwill be displaced by biological fluid and flow into plenum 930, and theninto outlet 927, into tubing 82, into receiving blood bag 99. Becausethe pressure at the bottom of upstream chamber 913 is greater than thepressure at the top of upstream chamber 913, the flow rate of biologicalfluid through the BFFM will be greater at the bottom of the BFFM than atthe top of the BFFM. Therefore, the BFFM will first become completelywetted from the upstream surface of the BFFM to the downstream surfaceof the BFFM at the bottom of BFFM. Once the bottom of the downstreamsurface of the sixth filter element has been wetted, the remainder ofthe downstream surface of the sixth filter element will continue to wetfrom the bottom up, and biological fluid will start to flow from thebottom of the sixth filter element, into plenum 930. The plenum willfill from the bottom up forcing the air above the liquid level in theplenum into outlet 927, into tubing 82, and then into receiving bloodbag 99. The plenum will fill with biological fluid before all of the airhas been purged from the upper portion of the BFFM. The remaining air inthe un-wetted upper portion of the BFFM will be displaced by biologicalfluid and forced into the plenum, where it will bubble to the top of theplenum due to the buoyancy of air in the biological fluid, and then beforced into outlet 927, into tubing 82, and then into receiving bloodbag 99 by the flow of biological fluid. Hence the initial flow ofbiological fluid through outlet 927, into tubing 82 will be a mixture ofair and biological fluid, so that the initial flow into tubing 82 willconsist of alternate segments of biological fluid and air.

Referring to FIG. 1, and FIG. 46, once all of the air has been purgedfrom within BFFD 1000, biological fluid will continue to flow throughthe first fluid flow path from the inlet of BFFD 1000 to the outlet ofBFFD 1000, and then through tubing 82 into receiving blood bag 99 untilfeed blood bag 98 is emptied of biological fluid. At this point feedblood bag 98 will be collapsed, effectively sealing the top of tubing81, thereby preventing the flow of biological fluid in tubing 81. Ifreceiving blood bag 99 is positioned at a level that is sufficientlylower than BFFD 1000, pressure P4 downstream of the BFFM and upstream ofoutlet 927 will be negative as described above. Therefore, thebiological fluid in tubing 83, tubing 81 a, and upstream chamber 913will be drained as described in the description of the first embodimentabove.

If the vent inlet, vent inlet slot, and vent tube socket (shown in FIG.13) are added to housing inlet half 901, BFFD 1000 could be used inbiological fluid filtration system 2000 shown in FIG. 12. In this caseBFFD 1000 would fill and purge air from within BFFD 1000 as justdescribed in the description of the tenth embodiment. After the air waspurged from BFFD 1000, it would function the same as BFFD 200 inbiological fluid filtration system 2000.

The filter under drain structure of BFFD 1000 including plenum 930 andvertical filter support ribs 922 may be replaced with the filter underdrain structure of the first embodiment shown in FIG. 3, in which casethe filter under drain structure would purge air and fill withbiological fluid as described in the description of the firstembodiment. If the filter under drain structure of the first embodimentis used to replace plenum 930 and vertical filter support ribs 922, thehold up volume of the BFFD will be minimized as explained in thedescription of the first embodiment, because of the lack of a plenum.

The filter under drain structure of BFFD 1000 including plenum 930 andvertical filter support ribs 922 may also be replaced with the filterunder drain structure of the second embodiment shown in FIG. 14, inwhich case the filter under drain structure would purge air and fillwith biological fluid as described in the description of the secondembodiment. If the filter under drain structure of the second embodimentis used to replace plenum 930 and vertical filter support ribs 922, theamount of air that will be purged from the BFFM after biological fluidstarts to flow from the outlet will be minimized, and the hold up volumeof the BFFD will also be minimized as explained in the description ofthe second embodiment, because of the lack of a plenum.

Detailed Description of the Eleventh Embodiment

An eleventh embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 49 through FIG.52. BFFD 1100 may be used in place of BFFD 100 in biological fluidfiltration system 1000 shown in FIG. 1, and may also be used in place ofBFFD 200 in biological fluid filtration system 2000 shown in FIG. 12.

Referring to FIG. 49, and FIG. 50, BFFD 1100 contains a rigid housingthat includes housing inlet half 801, housing inlet half 801 a, andhousing outlet half 1020. Housing inlet half 801, and 801 a are same ashousing inlet half 801 of the ninth embodiment. Housing seal surface 829a of housing inlet half 801, and of housing inlet half 801 a, are bondedto housing seal surface 1029 and housing seal surface 1029 arespectively, of housing outlet half 1020. The bond is preferably anultrasonic weld but may be a heat bond, a glue bond, a solvent bond, orany other type of leak tight bond.

Referring to FIG. 49, housing inlet half 801 and housing inlet half 801a are the same as housing inlet half 801 described in the description ofthe ninth embodiment. Flexible diaphragm 860 and flexible diaphragm 860a are the same as flexible diaphragm 860 described in the description ofthe ninth embodiment.

Referring to FIG. 49 through FIG. 52 housing outlet half 1020 contains apartition wall 1037 that divides BFFD 1100 into two independentfiltration devices having a common inlet, and a common outlet. On thefirst side of partition wall 1037 housing outlet half 1020 containsfirst filter well 1011 bounded by inner side wall 1008 and by firstfilter seal surface 1024, and second filter well 1011 a bounded by innerside wall 1008 a and by second filter seal surface 1024 a. First filterwell 1011 has a larger diameter than second filter well 1011 a. Thehorizontal center line of the first filter well is offset below thehorizontal center line of the second filter well so that the top offirst filter seal surface 1024 protrudes above the top of second filterseal surface 1024 a a sufficient distance to create a compression sealas will be described below. First filter well 1011 and second filterwell 1011 a are the same as first filter well 811 and second filter well811 a respectively of housing outlet half 820 of the ninth embodiment.Housing outlet half 1020 contains a third filter well and a fourthfilter well on the opposite side of partition wall 1037 that are mirrorimages of the first filter well and the second filter well respectively,mirrored about a plane that goes through the center of the partitionwall. Housing outlet half 1020 contains first circular outlet channel1025 and outlet 1027. First circular outlet channel 1025 is in directfluid flow communication with outlet 1027, and the portion of firstcircular outlet channel 1025 that adjoins outlet 1027 has across-sectional flow area that is greater than the cross-sectional flowarea of outlet 1027. Housing outlet half 1020 also contains a pluralityof open top closed bottom first vertical channels 1022 and 1022 a. Thetop end of each of the first vertical channels 1022 and 1022 a is influid flow communication with first circular outlet channel 1025. Thefirst vertical channels may be tapered in width and in depth as shown inFIG. 49 and FIG. 51, or they may be non-tapered like the verticalchannels of housing outlet half 120 shown in FIG. 15. The upper part offirst circular outlet channel 1025 increases in width to accommodate theflow of biological fluid from first vertical channels 1022 and 1022 a.The width of the remainder of first circular outlet channel 1025 (i.e.the lower part of first circular outlet channel 1025) is approximatelyequal to the width of the first vertical channels. The two outermostfirst vertical channels designated as first vertical channels 1022 aadjoin first circular outlet channel 1025 where the width of firstcircular outlet channel 1025 is approximately equal to the width of thefirst vertical channels. Upper side wall 1087 of first circular outletchannel 1025 preferably slopes upward toward outlet 1027 as shown inFIG. 51. The first circular outlet channel and the first verticalchannels combined, create a first filter under drain structure, and arecut into first inner wall 1021 of partition wall 1037, so that the innersurface of all of the first channels lies below first inner wall 1021,as shown in FIG. 50. The cross sectional area the first circular outletchannel and of the first vertical channels is defined by the innersurface of each channel and by the downstream surface of the first BFFM.Housing outlet half 1020 contains a second circular outlet channel and aplurality of open top closed bottom second vertical channels on thesecond side of partition wall 1037, that are in fluid flow communicationwith the second circular outlet channel, and cut into second inner wall1021 a of partition wall 1037. The second circular outlet channel andsecond vertical channels create a second filter under drain structurethat is a mirror image of the first filter under drain structure,mirrored about a plane that goes through the center of the partitionwall. The first circular outlet channel and the second circular outletchannel merge together at through slot 1025 b. Outlet 1027 is in directfluid flow communication with the first circular outlet channel and thesecond circular outlet channel where the two outlet channels merge. Asshown in FIG. 50 and FIG. 51, the distance between first verticalchannels 1022 and 1022 a is much greater than the width of firstvertical channels 1022 and 1022 a, and the distance between firstvertical channels 1022 and 1022 a is also much greater than of the depthof first vertical channels 1022 and 1022 a. Because housing outlet half1020 does not contain an open chamber or plenum downstream of the firstBFFM or downstream of the second BFFM, hold up volume is minimized.Housing outlet half 1020 also contains inlet 1005, a cross port labeledfirst cross port 1002 and second cross port 1002 a, first circulargroove 1088, second circular groove 1088 a, first slot 1004, and secondslot 1004 a. Inlet 1005 is in fluid flow communication with firstupstream chamber 1013 via first cross port 1002, first circular groove1088, and first slot 1004. Inlet 1005 is also in fluid flowcommunication with second upstream chamber 1013 a via second cross port1002 a, second circular groove 1088 a, and second slot 1004 a. The upperpart of first filter well 1011 contains a first seal ring counter borebounded by inner side wall 1008 b, and by surface 1024 b. The upper partof third filter well 1011 b contains a second seal ring counter borethat is a mirror image of the first seal ring counter bore, mirroredabout a plane that goes through the center of the partition wall.

Referring to FIG. 49 and FIG. 50, BFFD 1100 contains a first BFFM and asecond BFFM. The first BFFM is disposed in first filter well 1011 andsecond filter well 1011 a, and the second BFFM is disposed in thirdfilter well 1011 b and fourth filter well 1011 c. The first BFFM and thesecond BFFM are the same as the BFFM shown in FIG. 40 of the ninthembodiment, with the exception that there is an interference fit betweenthe perimeter surface of the second filter element of each of the BFFMand the inner side wall of housing outlet half 1020. Any of the BFFMwith the seating methods shown in FIG. 37 of the eighth embodiment, orin FIG. 40, 41, 42, or 45, of the ninth embodiment, or in FIG. 46 of thetenth embodiment, or any combination thereof could also be used in placeof the BFFM shown in FIG. 49.

Referring to FIG. 49, FIG. 50, and FIG. 51, a first fluid flow paththrough BFFD 1100 is defined between inlet 1005 of BFFD 1100 and outlet1027 of BFFD 1100 with the first BFFM interposed between inlet 1005 andoutlet 1027, and across the first fluid flow path. The first fluid flowpath flows from inlet 1005, through first cross port 1002, in bothdirections (as shown by arrows 1085 in FIG. 51) through first circulargroove 1088, through first slot 1004, into first upstream chamber 1013,through the first BFFM, into the first vertical channels and the firstcircular outlet channel, and then into outlet 1027. A second fluid flowpath through BFFD 1100 is defined between inlet 1005 of BFFD 1100 andoutlet 1027 of BFFD 1100 with the second BFFM interposed between inlet1005 and outlet 1027, and across the second fluid flow path. The secondfluid flow path flows from inlet 1005, through second cross port 1002 a,in both directions through the second circular groove 1088 a, throughsecond slot 1004 a, into second upstream chamber 1013 a, through thesecond BFFM, into the second vertical channels and the second circularoutlet channel, and then into outlet 1027.

Referring to FIG. 12, FIG. 49, and FIG. 50, when BFFD 1100 is used toreplace BFFD 200 in biological fluid filtration system 2000, the systemwill function as follows. The user will purchase the system with allcomponents as shown in FIG. 12, less feed blood bag 98. BFFD 1100 willreplace BFFD 200, and tubing 85 and vent filtration device 40 will notbe used. Because outlet tube socket 1028 is located at the top of BFFD1100, parallel to inlet tube socket 1006, tubing 82 will contain a loopto point downward toward receiving blood bag 99. The user will connecttubing 81 to outlet 92 of feed blood bag 98 in a manner known in theart. Feed blood bag 98 and vent filtration device 30, may be hung from ablood bag pole known in the art, and receiving blood bag 99 may beplaced on a table top or the like. Tube clamp 95 should be closed beforeconnecting tubing 81 to feed blood bag 98. Before opening tube clamp 95to start the flow of biological fluid through the system, tube clamp 96should be open, and tube clamp 97 should be closed.

Referring to FIG. 12, FIG. 49 through FIG. 52, BFFD 1100 functions asfollows. When tube clamp 95 is opened biological fluid (i.e. liquid)will flow from feed blood bag 98, through tubing 81, through the firstfluid flow path of BFFD 1100 by flowing into inlet 1005, through firstcross port 1002, through first circular groove 1088 in both directions(as shown by arrows 1085 in FIG. 51), through slot 1004, into firstupstream chamber 1013, of BFFD 1100. First upstream chamber 1013 willrapidly fill with biological fluid from the bottom up. As first upstreamchamber 1013 fills from the bottom up, the initial air in first upstreamchamber 1013 will be displaced by the biological fluid filling firstupstream chamber 1013. The displaced air will be forced through thefirst BFFM, into first vertical channels 1022 and 1022 a and firstcircular outlet channel 1025, and then into outlet 1027 all of BFFD1100. The biological fluid in first upstream chamber 1013 will bepressurized, with the pressure at the bottom of first upstream chamber1013 being proportional to the distance from the top of the biologicalfluid in feed blood bag 98 to the bottom of first upstream chamber 1013,and with the pressure at the top of first upstream chamber 1013 beingproportional to the distance from the top of the biological fluid infeed blood bag 98 to the top of first upstream chamber 1013. Hence thepressure at the top of first upstream chamber 1013 will be less than thepressure at the bottom of first upstream chamber 1013. The positivepressure in first upstream chamber 1013 will cause the biological fluidto flow through first filter element 815, and second filter element 816over the entire surface area of the first and second filter elementsdisplacing the air within the pores of the first and second filterelements with biological fluid, thereby wetting the first and secondfilter elements from the upstream side of first filter element 815 tothe downstream side of second filter element 816. The displaced air fromfirst upstream chamber 1013 and from the first and second filterelements will flow into third filter element 817. Third filter element817 preferably has an open pore size and structure that allows flowthrough it in all directions. Therefore any air or biological fluid thatflows from the downstream surface of second filter element 816, willflow into third filter element 817 and then be uniformly distributedover the entire upstream surface of fourth filter element 818, therebyutilizing fourth filter element 818 in the most efficient way. As thefirst and second filter elements wet, the air that was initially in thepores of the first and second filter elements will be displaced bybiological fluid, and flow into the third filter element 817. Becausethe pressure at the bottom of first upstream chamber 1013 is greaterthan the pressure at the top of first upstream chamber 1013, the flowrate of biological fluid through the first and second filter elementswill be greater at the bottom of the first and second filter elementsthan at the top of the first and second filter elements. Therefore, thefirst and second filter elements will first become completely wettedfrom the upstream surface of the first filter element to downstreamsurface of the second filter element at the bottom of the second filterelement. The first and second filter elements will continue to wet withthe downstream surface of the second filter element wetting from thebottom to the top. The third filter element will also wet from thebottom to the top. When the liquid level in the third filter elementreaches the bottom of fourth filter element 818, the fourth filterelement will begin to wet from the bottom up. The first and secondfilter elements will continue to wet until all of the air in the firstand second filter elements has been purged. It is important that thehorizontal center line of first filter well 1011 is offset the requireddistance below the horizontal center line of second filter well 1011 aso that the top of first filter seal surface 1024 protrudes above thetop of second filter seal surface 1024 a no more than the distancerequired to create a compression seal at the top of the first filterwell between seal ring 1050 and first filter seal surface 1024 ofhousing outlet half 1020, because air will be trapped in the compressionseal portion of the first, second, and third filter elements that lieabove horizontal line 1076 shown in FIG. 49. The fourth, fifth, andsixth filter elements will wet from the bottom up, with the downstreamsurface of the sixth filter element first becoming wetted at the bottomof the downstream surface of the sixth filter element. If the width ofvertical channels 1022 and 1022 a is sufficiently small, and the depthof vertical channels 1022 and 1022 a is sufficiently shallow, so thatthe cross-sectional flow area of the vertical channels 1022 and 1022 ais sufficiently small, and if the distance between vertical channels1022 and 1022 a is sufficiently large, as described above in thedescription of the second embodiment, the path of least resistance forcontinued biological fluid flow through the first BFFM will be throughthe capillaries of the first BFFM in both the horizontal and verticaldirections and not through the first vertical channels, because if thecross-sectional flow area of the first vertical channels is sufficientlysmall, the displaced air flowing into and through the first verticalchannels will create a sufficiently high positive pressure in the firstvertical channels to prevent biological fluid from entering the firstvertical channels. The downstream surface of the first BFFM (i.e. thedownstream surface of the sixth filter element) will therefore wet fromthe bottom up and the displaced air that was within the first BFFM willcontinue to flow into the first vertical channels, and into the firstcircular outlet channel, and then into the outlet. When the downstreamsurface of the first BFFM has become wetted to the level of the upperpart of first circular outlet channel 1025 where first circular outletchannel 1025 begins to taper to a wider width, air flow through thelower part of first circular outlet channel 1025, and air flow throughthe two outermost first vertical channels 1022 a will stop because thedownstream surface of the first BFFM adjoining the lower part of thefirst circular outlet channel and the two outermost first verticalchannels will be wetted. Therefore the pressure in the lower part of thefirst circular outlet channel and the pressure in the two outermostfirst vertical channels will decrease allowing biological fluid to enterthe lower part of the first circular outlet channel and the twooutermost first vertical channels from the bottom up, thereby displacingthe air that was in the lower part of the first circular outlet channeland the two outermost first vertical channels. At the same time thewetted level of the downstream surface of the first BFFM will continueto wet in the vertical direction, wetting the downstream surface of thefirst BFFM adjoining the upper part of first circular outlet channel1025. Because the cross-sectional flow area of the upper part of firstcircular outlet channel 1025 is not sufficiently small to create apositive pressure in it due to the air flow through it, biological fluidwill flow into first circular outlet channel 1025 as first BFFMcontinues to wet in the vertical direction above the lower part of thefirst circular outlet channel. The biological fluid flowing into firstvertical channels 1022 and 1022 a, and into the first circular outletchannel 1025 will flow into outlet 1027 of BFFD 1100 and then intotubing 82 toward receiving blood bag 99. As biological fluid starts toflow into outlet 1027, first BFFM will continue to wet vertically. Whentube clamp 95 is opened biological fluid will also flow from feed bloodbag 98, through tubing 81, through the second fluid flow path of BFFD1100 the same way that it flows through the first fluid flow path ofBFFD 1100, and the second BFFM will wet, and air will be purged from itas just described for the first fluid flow path of BFFD 1100. Hence theinitial flow of biological fluid through the upper part of firstcircular outlet channel 1025, and through the upper part of secondcircular outlet channel 1025 a, and through outlet 1027, will be amixture of air and biological fluid so that the initial flow into tubing82 will consist of alternate segments of biological fluid and air. Asdescribed in the description of the second embodiment above, the amountof biological fluid that flows from outlet 1027 will be minimizedbecause of the design of the first and second filter under drainstructures, and because of the reduced surface area of the fourth,fifth, and sixth filter elements of the first BFFM and of the secondBFFM.

Referring to FIG. 12, and FIG. 49, once all of the air has been purgedfrom within BFFD 1100, biological fluid will continue to flow throughthe first fluid flow path from the inlet of BFFD 1100 to the outlet ofBFFD 1100, and through the second fluid flow path from the inlet of BFFD1100 to the outlet of BFFD 1100, and then through tubing 82 intoreceiving blood bag 99 until feed blood bag 98 is emptied of biologicalfluid. At this point feed blood bag 98 will be collapsed, effectivelysealing the top of tubing 81, thereby preventing the flow of biologicalfluid in tubing 81. If receiving blood bag 99 is positioned at a levelthat is sufficiently lower than BFFD 1100, pressure P5 downstream of thefirst BFFM and downstream of the second BFFM, and upstream of outlet1027 will be negative as described above in the description of thesecond embodiment. Once feed blood bag 98 collapses and biological fluidflow through the first fluid flow path and the second fluid flow path ofBFFD 1100 stops, the differential pressure across the first BFFM, andthe differential pressure across the second BFFM, will become zero,hence the pressure in first upstream chamber 1013 and second upstreamchamber 1013 a will become negative. The pressure on upstream surface866 of flexible diaphragm 860 and on upstream surface 866 of flexiblediaphragm 860 a will be atmospheric because hole 871 of housing inlethalf 801 and hole 871 of housing inlet half 801 a are open toatmosphere, and hole 871 is in fluid flow communication with radial ventchannel 803 a, and circular vent channels 803 of housing inlet half 801and housing inlet half 801 a. With atmospheric pressure on the outersurface 866 of flexible diaphragm 860, the negative pressure withinfirst upstream chamber 1013 will cause flexible diaphragm 860 tocollapse onto the upstream surface of first filter element 815, therebyforcing the biological fluid in first upstream chamber 1013 through thefirst BFFM, into the first vertical channels and into the first circularoutlet channel, into outlet 1027, into tubing 82, and then intoreceiving blood bag 99. Also, with atmospheric pressure on the outersurface 866 of flexible diaphragm 860 a, the negative pressure withinsecond upstream chamber 1013 a will cause flexible diaphragm 860 a tocollapse onto the upstream surface of first filter element 815 a,thereby forcing the biological fluid in second upstream chamber 1013 athrough the second BFFM, into the second vertical channels and into thesecond circular outlet channel, into outlet 1027, into tubing 82, andthen into receiving blood bag 99.

Referring to FIG. 12, and FIG. 49, when the filtration cycle is completeas just described, the first BFFM and the second BFFM will remainwetted, the first vertical channels and first circular outlet channeland the second vertical channels and second circular outlet channel willbe filled with biological fluid, and tubing 82 will be filled withbiological fluid. Because BFFD 1100 does not contain a plenum downstreamof the first BFFM or downstream of the second BFFM, the hold up volumeof biological fluid within BFFD 1100 will be minimized. The user willclose tube clamp 96, and then cut and seal tubing 82 above tube clamp96, and then discard BFFD 1100 and feed blood bag 98 in a safe manner.Tube clamp 97 may now be opened, and the air in receiving blood bag 99may be purged from receiving blood bag 99 by squeezing receiving bloodbag 99 thereby forcing the air in receiving blood bag 99 through thethird fluid flow path from vent port 91 of receiving blood bag 99 toatmosphere. Tubing 84 can then be sealed and cut near receiving bloodbag 99, and then tubing 84 and vent filtration device 30 may bediscarded in a safe manner.

Detailed Description of the Twelfth Embodiment

A twelfth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 53 through FIG.56. BFFD 1200 may be used in place of BFFD 200 in biological fluidfiltration system 2000 shown in FIG. 12.

Referring to FIG. 53 through FIG. 56, BFFD 1200 contains a rigid housingthat includes housing inlet half 1101, housing inlet half 1101 a, andhousing outlet half 1120. Housing inlet half 1101, and 1101 a are sameas housing inlet half 901 of the tenth embodiment except that housinginlet half 1101 and 1101 a may or may not contain circular rib 989 shownin FIG. 48. Housing inlet halves 1101 and 1101 a are bonded to housingoutlet half 1120 in the same way that housing inlet half 901 is bondedto housing outlet half 920 as described in the description of the tenthembodiment above. Housing outlet half 1120 is the same as housing outlethalf 1020 of the eleventh embodiment with the following exceptions.Vertical channels 1122 and 1122 a and circular outlet channel 1125 arelocated on the first side of partition wall 1138, and are cut into firstinner wall 1121. Vertical channels 1122 and 1122 a are the same asvertical channels 1022 and 1022 a, and may be tapered in width and/ordepth as shown, or may be non tapered like vertical channels 122 and 122a shown in FIG. 14. Circular outlet channel 1125 has a constant width,with the portion of circular outlet channel 1125 adjoining outlet 1127increasing in depth, and having a cross sectional flow area greater thanthe cross sectional flow area of outlet 1127. Vertical channels 1122 band 1122 c are located on the second side of partition wall 1138, andare cut into second inner wall 1121 a. The vertical center lines ofvertical channels 1122 b and 1122 c are offset from the verticalcenterlines of vertical channels 1122 and 1122 a, so that the verticalcenter lines of vertical channels 1122 b and 1122 c are located betweenthe vertical center lines of vertical channels 1122 and 1122 a, as shownin FIG. 53. Ports 1172 place the tops of vertical channels 1122 b and1122 c in fluid flow communication with circular outlet channel 1125.Circular outlet channel 1125 provides a means to place the tops ofvertical channels 1122, 1122 a, 1122 b, and 1122 c in fluid flowcommunication with outlet 1127 located below the bottom of circularoutlet channel 1125. Because the second side of partition wall 1138 doesnot contain a circular outlet channel, and because the vertical channelson the second side of partition wall are offset from the verticalchannels on the first side of partition wall 1138, partition wall 1138may be made thinner than would otherwise be the case, thereby reducingthe cost of producing housing outlet half 1120. Housing outlet half 1120also contains vent inlet 1178 that is in fluid flow communication withfirst cross port 1102 and with second cross port 1102 a.

Referring to FIG. 55 and FIG. 56, BFFD 1200 contains a first BFFM and asecond BFFM. The first BFFM is disposed in first filter well 1111 andsecond filter well 1111 a, and the second BFFM is disposed in thirdfilter well 1111 b and fourth filter well 1111 c. The first BFFM and thesecond BFFM each contain six filter elements. None of the filterelements has an interference fit between the perimeter surface of thefilter element and its respective inner side wall of housing outlet half1120. The outer periphery of the filter elements in first filter well1111 are bonded to each other and to filter seal surface 1124 by bond1177, and the outer periphery of the filter elements in second filterwell 1111 a are bonded to each other and to filter seal surface 1124 aby bond 1176. Likewise, the outer periphery of the filter elements inthird filter well 1111 b are bonded to each other and to filter sealsurface 1124 b by bond 1177 a, and the outer periphery of the filterelements in third filter well 1111 c are bonded to each other and tofilter seal surface 1124 c by bond 1176 a. The bonds may be a glue bond,a heat bond, an ultrasonic bond, a solvent bond, an R.F. bond, or anyother type of leak tight bond. Any of the BFFM with the sealing methodsshown in FIG. 37 of the eighth embodiment, or in FIG. 40, 41, 42, or 45,of the ninth embodiment, or in FIG. 46 of the tenth embodiment, or inFIG. 49 of the eleventh embodiment, or any combination thereof couldalso be used in place of the BFFM's shown in FIG. 55.

Referring to FIG. 53 through FIG. 56, a first fluid flow path throughBFFD 1200 is defined between inlet 1105 of BFFD 1200 and outlet 1227 ofBFFD 1200 with the first BFFM interposed between inlet 1105 and outlet1127, and across the first fluid flow path. The first fluid flow pathflows from inlet 1105, through first cross port 1002, in both directionsthrough first circular groove 1188, through first slot 1104, into firstupstream chamber 1113, through the first BFFM, into first verticalchannels 1122 and 1122 a, through circular outlet channel 1125, and theninto outlet 1127. A second fluid flow path through BFFD 1200 is definedbetween inlet 1105 of BFFD 1200 and outlet 1127 of BFFD 1200 with thesecond BFFM interposed between inlet 1105 and outlet 1127, and acrossthe second fluid flow path. The second fluid flow path flows from inlet1105, through second cross port 1102 a, in both directions through thesecond circular groove 1188 a, through second slot 1104 a, into secondupstream chamber 1113 a, through the second BFFM, into the secondvertical channels 1122 b and 1122 c, through ports 1172, throughcircular outlet channel 1125, and then into outlet 1127.

Referring to FIG. 12, FIG. 55, and FIG. 56, when BFFD 1200 is used toreplace BFFD 200 in biological fluid filtration system 2000, the systemwill function as follows. The user will purchase the system with allcomponents as shown in FIG. 12, less feed blood bag 98. BFFD 1200 willreplace BFFD 200. The BFFD end of tubing 85 will be connected to venttube socket 1179. The user will connect tubing 81 to outlet 92 of feedblood bag 98 in a manner known in the art. Feed blood bag 98, ventfiltration device 40, and vent filtration device 30, may be hung from ablood bag pole known in the art, and receiving blood bag 99 may beplaced on a table top or the like. Tube clamp 95 should be closed beforeconnecting tubing 81 to feed blood bag 98. Before opening tube clamp 95to start the flow of biological fluid through the system, tube clamp 96and tube clamp 94 should be open, and tube clamp 97 should be closed.

Referring to FIG. 12, FIG. 53 through FIG. 56, BFFD 1200 functions asfollows. When tube clamp 95 is opened biological fluid will flow fromfeed blood bag 98, through tubing 81, through the first fluid flow pathof BFFD 1200 by flowing into inlet 1105, through first cross port 1102,through first circular groove 1188 in both directions, through slot1104, into first upstream chamber 1113, of BFFD 1200. First upstreamchamber 1113 will fill from the bottom up displacing the air that was infirst the upstream chamber, and wetting the first BFFM as describedabove in the description of the eleventh embodiment. Once the bottom ofthe downstream surface of the first BFFM has become wetted, thedownstream surface of the first BFFM will continue to wet from thebottom up, until the downstream surface of the first BFFM has becomewetted to the level of the top of first vertical channels 1122 a. Atthis point biological fluid will begin to flow into vertical channels1122 a from the bottom up. As the downstream surface of the first BFFMcontinues to wet vertically, biological fluid will begin to flow intosuccessive vertical channels as the wetted level of the downstreamsurface of the first BFFM reaches the top of each vertical channel. Ifcircular outlet channel 1125 is sufficiently wide, a small quantity ofbiological fluid may enter circular outlet channel 1125 before thewetted level of the downstream surface of the first BFFM reaches the topof vertical channels 1122 a. When tube clamp 95 is opened biologicalfluid will also flow from feed blood bag 98, through tubing 81, throughthe second fluid flow path of BFFD 1200 by flowing into inlet 1105,through second cross port 1102 a, through second circular groove 1188 ain both directions, through slot 1104 a, into second upstream chamber1113 a, of BFFD 1200. Second upstream chamber 1113 a will fill from thebottom up displacing the air that was in the second upstream chamber,and wetting the second BFFM as described above in the description of theeleventh embodiment. Once the bottom of the downstream surface of thesecond BFFM has become wetted, the downstream surface of the second BFFMwill continue to wet from the bottom up, until the downstream surface ofthe second BFFM has become wetted to the level of the top of secondvertical channels 1122 c. At this point biological fluid will begin toflow into second vertical channels 1122 c from the bottom up. As thedownstream surface of the second BFFM continues to wet vertically,biological fluid will begin to flow into successive vertical channels asthe wetted level of the downstream surface of the second BFFM reachesthe top of the second vertical channels. The air and biological fluidthat flows into the second vertical channels will flow through ports1172, into circular outlet channel 1125, and then into outlet 1127. Allof the air will be purged from within BFFD before the pressure P6downstream of the first BFFM and second BFFM, and upstream of outlet1127 becomes negative.

Referring to FIG. 10, FIG. 12, and FIG. 55, once all of the air has beenpurged from within BFFD 1200, biological fluid will continue to flowthrough the first fluid flow path from the inlet of BFFD 1200 to theoutlet of BFFD 1200, and through the second fluid flow path from theinlet of BFFD 1200 to the outlet of BFFD 1200, and then through tubing82 into receiving blood bag 99 until feed blood bag 98 is emptied ofbiological fluid. At this point feed blood bag 98 will be collapsed,effectively sealing the top of tubing 81, thereby preventing the flow ofbiological fluid in tubing 81. If receiving blood bag 99 is positionedat a level that is sufficiently lower than BFFD 1200, pressure P6downstream of the first BFFM and downstream of the second BFFM, andupstream of outlet 1127 will be negative as described above in thedescription of the second embodiment. Vent port 46 of vent filtrationdevice 40 is at atmospheric pressure, therefore, there will be apressure differential between vent port 46 and the negative pressure P6downstream of the BFFM. The pressure differential will cause air to flowfrom vent port 46, through vent filtration media 43, through system port44, all of vent filtration device 40, through tubing 85, through ventinlet 1178 of BFFD 1200, through first cross port 1102, into firstupstream chamber 1133, thereby draining the biological fluid in firstupstream chamber 1113 of BFFD 1200. Air will also flow from inlet 1105,through second cross port 1102 a, into second upstream chamber 1113 a,thereby draining the biological fluid in second upstream chamber 1113 aof BFFD 1200.

Referring to FIG. 12, and FIG. 55, when the filtration cycle is completeas just described, the first BFFM and the second BFFM will remainwetted, the first vertical channels and circular outlet channel and thesecond vertical channels will be filled with biological fluid, andtubing 82 will be filled with biological fluid. Because BFFD 1200 doesnot contain a plenum downstream of the first BFFM or downstream of thesecond BFFM, the hold up volume of biological fluid within BFFD 1200will be minimized. The user will close tube clamp 96, and then cut andseal tubing 82 above tube clamp 96, and then discard BFFD 1200 and thecomponents attached to it in a safe manner. Tube clamp 97 may now beopened, and the air in receiving blood bag 99 may be purged fromreceiving blood bag 99 by squeezing receiving blood bag 99 therebyforcing the air in receiving blood bag 99 through the third fluid flowpath from vent port 91 of receiving blood bag 99 to atmosphere. Tubing84 can then be sealed and cut near receiving blood bag 99, and thentubing 84 and vent filtration device 30 may be discarded in a safemanner.

Detailed Description of the Thirteenth Embodiment

A thirteenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 57 and FIG. 58.BFFD 1300 may be used in place of BFFD 200 in biological fluidfiltration system 2000 shown in FIG. 12.

Referring to FIG. 57, BFFD 1300 contains a flexible housing thatincludes flexible housing inlet half 1201 and flexible housing outlethalf 1220. Housing seal surface 1229 a of housing inlet half 1201 isbonded to housing seal surface 1229 of housing outlet half 1220. Thebond is preferably an ultrasonic weld but may be a heat bond, a gluebond, a solvent bond, R.F. bond, or any other type of leak tight bond.Housing inlet half contains inlet 1205 and inlet tube socket 1206.Housing outlet half 1220 contains outlet 1227 and outlet tube socket1228.

Referring to FIG. 57, the BFFM contains four filter elements, firstfilter element 1215, second filter element 1216, third filter element1217, and fourth filter element 1218. Any of the filter elements maycontain one or more layers of the filter material of the same type. Thefirst filter element has a pore size greater than the pore size of thesecond filter element, and the fourth filter element has a pore sizesmaller than the pore size of the second filter element, while the poresize of the third filter element has a pore size greater than the poresize of the second filter element. Preferably the pore size of the thirdfilter element is greater than the pore size of the first and secondfilter elements. When BFFD 1300 is used to filter blood or bloodproduct, first filter element 1215 may be sized to remove gels from theblood or blood product, second filter element 1216 may be sized toremove microaggregates from the blood or blood product, fourth filterelement 1218 may be sized to remove leukocytes from the blood or bloodproduct, while the third filter element 1217 is sized to act as a flowdistribution layer. Because gels and microaggregates are large particlesthey may clump together thereby reducing the flow through thegel-microaggregate filter elements in the region of the clump. The flowdistribution filter element will distribute the effluent from themicroaggregate filter element evenly over the upstream surface of theleukocyte removing layer, thereby allowing the leukocyte removing layerto be utilized most efficiently. The outside diameter of all of thefilter elements as shown in FIG. 57 are smaller than the inside diameterof flexible housing outlet half 1220, preventing the filter elementsfrom being sealed to BFFD 1300 with an interference fit between theperimeter surface of filter elements and inner side wall of flexiblehousing outlet half 1220. The outer periphery of each filter element isbonded to the outer periphery of the filter element adjacent to it, withthe outer periphery of the downstream surface of the BFFM being bondedto flexible housing outlet half 1220 as shown in FIG. 57. The bonds maybe a glue bond, a heat bond, an ultrasonic bond, an R.F. bond, a solventbond, or any other type of leak tight bond. Third filter element 1217 ispreferably a woven or non-woven screen filter, but could be any type ofopen pore size depth filter. The main purpose of filter element 1217 isflow distribution therefore it has a large pore size, and is preferablystructured to allow flow through it in all directions. In applicationswhere the blood or blood product is fresh and does not contain gels, thefirst filter element may be a microaggregate removing filter element,and the second filter element could be eliminated. In this case thethird filter element may also be eliminated.

BFFD 1300 also contains filter support screen 1277. Filter supportscreen 1277 is preferably a woven or non-woven screen that is structuredto allow flow through it in all directions, and does not perform anyfiltration functions. The pore size of filter support screen 1277 islarger than the pore size of the fourth filter element.

Referring to FIG. 57 a first fluid flow path is defined between inlet1205 of BFFD 1300 and outlet 1227 of BFFD 1300, with the BFFM interposedbetween inlet 1205 and outlet 1227, and across the fluid flow path. Thefirst fluid flow path flows from inlet 1205, into upstream chamber 1213,through the BFFM, into outlet 127.

Referring to FIG. 12 and FIG. 57, when BFFD 1300 is used to replace BFFD200 in biological fluid filtration system 2000, the system will functionas follows. The user will purchase the system with all components asshown in FIG. 12, less feed blood bag 98. BFFD 1300 will replace BFFD200, tubing 85 and vent filtration device 40 will not be used. The userwill connect tubing 81 to outlet 92 of feed blood bag 98 in a mannerknown in the art. Feed blood bag 98 and vent filtration device 30, maybe hung from a blood bag pole known in the art, and receiving blood bag99 may be placed on a table top or the like. Tube clamp 95 should beclosed before connecting tubing 81 to feed blood bag 98. Before openingtube clamp 95 to start the flow of biological fluid through the system,tube clamp 96 should be open, and tube clamp 97 should be closed.

Referring to FIG. 12, and FIG. 57, BFFD 1300 functions as follows. Whentube clamp 95 is opened biological fluid will flow from feed blood bag98, through tubing 81, into inlet 1205 of BFFD 1300 and then intoupstream chamber 1213 of BFFD 1300. Upstream chamber 1213 will rapidlyfill with biological fluid from the bottom up. As upstream chamber 1213fills from the bottom up, the initial air in upstream chamber 213 willbe displaced by the biological fluid filling upstream chamber 1213. Thedisplaced air will be forced through the BFFM, into filter supportscreen 1277. Because the filter support screen 1277 is a woven ornon-woven screen with a large pore size that allows flow in alldirections, the displaced air will flow through filter support screenfilter 1277 into outlet 1227. The biological fluid in upstream chamber1213 will be pressurized, with the pressure at the bottom of upstreamchamber 1213 being proportional to the distance from the top of thebiological fluid in feed blood bag 98 to the bottom of upstream chamber1213, and with the pressure at the top of upstream chamber 1213 beingproportional to the distance from the top of the biological fluid infeed blood bag 98 to the top of upstream chamber 1213. Hence thepressure at the top of upstream chamber 1213 will be less than thepressure at the bottom of upstream chamber 1213. The positive pressurein upstream chamber 1213 will cause the biological fluid to flow throughthe BFFM over the entire surface area of the BFFM and to displace theair within the pores of the BFFM with biological fluid, thereby wettingBFFM from the upstream side of the BFFM to the downstream side of theBFFM. As the BFFM wets the air that was initially in the pores of BFFMwill be displaced by biological fluid and flow into the filter supportscreen, and then into outlet 1227, into tubing 82, and then intoreceiving blood bag 99. Because the pressure at the bottom of upstreamchamber 1213 is greater than the pressure at the top of upstream chamber1213, the flow rate of biological fluid through the BFFM will be greaterat the bottom of the BFFM than at the top of the BFFM. Therefore theBFFM will first become completely wetted from the upstream surface ofBFFM to downstream surface of the BFFM at the bottom of the BFFM. TheBFFM will continue to wet from the bottom up, with biological fluidflowing from the portions of the BFFM where the downstream surface hasbeen wetted, into the filter support screen, and with air flowing intothe filter support screen from the portions of the BFFM where thedownstream surface has not been wetted. Therefore, the initial flow ofbiological fluid into tubing 82 will consist of alternate segments ofbiological fluid and air.

Referring to FIG. 12, and FIG. 57, once all of the air has been purgedfrom within BFFD 1300, biological fluid will continue to flow throughthe first fluid flow path from the inlet of BFFD 1300 to the outlet ofBFFD 1300, and then through tubing 82 into receiving blood bag 99 untilfeed blood bag 98 is emptied of biological fluid. At this point feedblood bag 98 will be collapsed, effectively sealing the top of tubing81, thereby preventing the flow of biological fluid in tubing 81. Ifreceiving blood bag 99 is positioned at a level that is sufficientlylower than BFFD 1300, pressure P7 downstream of the BFFM and upstream ofoutlet 1227 will be negative. Once feed blood bag 98 collapses andbiological fluid flow through the first fluid flow path stops thedifferential pressure across the BFFM will become zero, hence thepressure in upstream chamber 1213 will become negative. The pressure onouter surface of flexible housing inlet half 1201 will be atmospheric.With atmospheric pressure on the outer surface of flexible housing inlethalf 1201, the negative pressure within upstream chamber 1213 will causeflexible housing inlet half 1201 to collapse onto the upstream surfaceof the BFFM, thereby forcing the biological fluid in upstream chamber1213 through the BFFM, into filter support screen 1277, into outlet1227, into tubing 82, and then into receiving blood bag 99.

Referring to FIG. 12, and FIG. 57, when the filtration cycle is completeas just described, the BFFM will remain wetted, the filter supportscreen will be filled with biological fluid, and tubing 82 will befilled with biological fluid. The user will close tube clamp 96, andthen cut and seal tubing 82 above tube clamp 96, and then discard BFFD1300 and feed blood bag 98 in a safe manner. Tube clamp 97 may now beopened, and the air in receiving blood bag 99 may be purged fromreceiving blood bag 99 by squeezing receiving blood bag 99 therebyforcing the air in receiving blood bag 99 through the third fluid flowpath from vent port 91 of receiving blood bag 99 to atmosphere. Tubing84 can then be sealed and cut near receiving blood bag 99, and thentubing 84 and vent filtration device 30 may be discarded in a safemanner.

FIG. 58 shows BFFD 1300 with the perimeter surface of filter elementsbonded to one another, and also bonded to the inner side wall of housingoutlet half 1220. The bonds may be a glue bond, a heat bond, anultrasonic bond, an R.F. bond, a solvent bond, or any other type of leaktight bond. BFFD 1300 shown in FIG. 58 functions the same as BFFD 1300shown in FIG. 57.

Detailed Description of the Fourteenth Embodiment

A fourteenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 59 and FIG. 60.BFFD 1400 may be used in place of BFFD 100 in biological fluidfiltration system 1000 shown in FIG. 1, or it may be used in place ofBFFD 200 in biological fluid filtration system 2000 shown in FIG. 12.

Referring to FIG. 59, and FIG. 60, BFFD 1400 contains a rigid housingthat includes housing inlet half 101 a and housing outlet half 1320.Housing seal surface 129 a of housing inlet half 101 a is bonded tohousing seal surface 1329 of housing outlet half 1320. The bond ispreferably an ultrasonic weld but may be a heat bond, a glue bond, asolvent bond, or any other type of leak tight bond.

Housing inlet half 101 a is the same as housing inlet half 101 of thesecond embodiment shown in FIG. 13 with the exception that inlet 105 ofhousing inlet half 101 a is located below the center line of housinginlet half 101 a, and vent inlet of housing inlet half 101 a is locatedabove the center line of housing inlet half 101 a.

Referring to FIG. 14, FIG. 44, FIG. 59, and FIG. 60, housing outlet half1320 contains first filter well 1311 and second filter well 1311 a thatare the same as first filter well 811 and second filter well of housingoutlet half 820 shown in FIG. 44. First filter well 1311 has a largerdiameter than second filter well 1311 a. The horizontal center line ofthe first filter well is offset below the horizontal center line of thesecond filter well so that the top of first filter seal surface 1324protrudes above the top of second filter seal surface 1324 a asufficient distance to create a compression seal, and so that theperimeter of the second filter well is located entirely within theperimeter of the first filter well. The filter under drain structure ofhousing outlet half 1320 comprised of vertical channels 122 and 122 a,and circular outlet channel 125, is the same as the filter underdrainstructure of housing outlet half 120 of the second embodiment shown inFIG. 14, with the exception that there are fewer vertical channels inhousing outlet half 1320 because of the reduced surface area of thefilter elements in the second filter well.

Referring to FIG. 59 and FIG. 60, the BFFM contains four filterelements, first filter element 815, second filter element 816, thirdfilter element 817, and fourth filter element 818 comprised of fourlayers of filter material of the same type. Any of the filter elementsmay contain one or more layers of the filter material of the same type.The first filter element has a pore size greater than the pore size ofthe second filter element, the fourth filter element has a pore sizesmaller than the pore size of the second filter element, while the thirdfilter element has a pore size greater than the pore size of the secondfilter element. Preferably the pore size of the third filter element isgreater than the pore size of the first and second filter elements. WhenBFFD 1400 is used to filter blood or blood product, first filter element815 may be sized to remove gels from the blood or blood product, secondfilter element 816 may be sized to remove microaggregates from the bloodor blood product, fourth filter element 818 may be sized to removeleukocytes from the blood or blood product, while the third filterelement 817 is sized to act as a flow distribution layer. Because gelsand microaggregates are large particles they may clump together therebyreducing the flow through the gel-microaggregate filter elements in theregion of the clump. The flow distribution filter element willdistribute the effluent from the microaggregate filter element evenlyover the upstream surface of the leukocyte removing layer, therebyallowing the leukocyte removing layer to be utilized most efficiently.Once the gels and microaggregates have been removed from the blood orblood product, the blood or blood product will be relatively clean andtherefore the surface area of the leukocyte removing layer may be madesmaller than the surface area of the gel and microaggregate layers,thereby reducing the hold up volume of the BFFD. The gel filter element,and the microaggregate filter element, and the first flow distributionfilter element, are inserted into the first filter well of housingoutlet half 1320. Gel filter element 815, and flow distribution filterelement 817, have outside diameters smaller than the inside diameter ofinner side wall 808, preventing them from being sealed to BFFD 900 withan interference fit between the perimeter surface of each respectivefilter element and inner side wall 1308 of housing outlet half 1320. Theouter periphery of the gel filter element is sealed to the housing witha compression seal, by compressing the outer periphery of the gel filterelement with filter seal surface 107 of housing inlet half 101 a.Alternately the gel filter element could have an outside diameter largeenough so that it could be sealed to the housing an interference fitbetween the perimeter surface of the gel filter element and inner sidewall 1308 of housing outlet half 1320, and the microaggregate filterelement could have an outside diameter smaller than the inside diameterof inner side wall 1308, or both the gel filter element and themicroaggregate filter element could have outside diameters smaller thanthe inside diameter of inner side wall 1308. Third filter element 817 ispreferably a woven or non-woven screen filter, but could be any type ofopen pore size depth filter, or any other type of structure that allowsflow in all directions. The main purpose of flow distribution filterelement 817 is flow distribution, therefore it preferably has a poresize large enough so that it will not retain gels, microaggregates, orleukocytes, and is preferably structured to allow flow through it in alldirections. Hence the perimeter surface of filter element 817 need nothave an interference fit with inner side wall 1308. Housing outlet half820 also contains a second filter well smaller in diameter than thefirst filter well into which leukocyte removing filter element 818 isinserted. Leukocyte removing filter element 818 is sealed to the housingan interference fit between the perimeter surface of each layer of theleukocyte removing filter material and inner side wall 1308 a of housingoutlet half 1320. Alternately, if the blood or blood product isrelatively clean, gel filter element 815 may be followed by flowdistribution filter element 817, with both filter elements beinginserted into the first filter well, and microaggregate filter element816, could follow flow distribution filter element 817, with themicroaggregate filter element having a smaller diameter so that it couldbe inserted into the second filter well on top of the leukocyte removingfilter element. Another alternative would be to make filter element 815a gel or microaggregate removing filter element, and to make filterelement 816 a first leukocyte removing filter element, with filterelement 817 being a flow distribution filter element, and with filterelement 818 being a second leukocyte filter element. Yet anotheralternative would to add a fourth filter element to the first filterwell in-between filter element 816 and filter element 817, in which casefilter element 815 would be a gel removing filter element, filterelement 816 would be a microaggregate removing filter element, thefourth filter element in the first filter well would be a firstleukocyte removing filter element and filter element 818 would be asecond leukocyte removing filter element. Any of the BFFM with thesealing methods shown in FIG. 37 of the eighth embodiment, or in FIG.40, 41, 42, or 45, of the ninth embodiment, or in FIG. 46 of the tenthembodiment, or in FIG. 49 of the eleventh embodiment, or in FIG. 55 ofthe twelfth embodiment, or any combination thereof could also be used inplace of the BFFM shown in FIG. 59.

Referring to FIG. 59, a first fluid flow path is defined between inlet105 of BFFD 1400 and outlet 1327 of BFFD 1400 with the BFFM interposedbetween inlet 105 and outlet 1327, and across the fluid flow path. Thefirst fluid flow path flows from inlet 105, through inlet slot 102, intoupstream chamber 1313, through the BFFM, into vertical channels 122 and122 a, into circular outlet channel 125, and then into outlet 827.

BFFD 1400 can be used to replace BFFD 100 in biological fluid filtrationsystem 1000 shown in FIG. 1, or it may be used to replace BFFD 200 inbiological fluid filtration system 2000 shown in FIG. 12. In either caseBFFD 1400 will function as follows. When tube clamp 95 is openedbiological fluid will flow from feed blood bag 98 as described in thefirst and second embodiments above, through the first fluid flow path ofBFFD 1400 by flowing into inlet 105, through inlet slot 102, intoupstream chamber 1313, of BFFD 1400. Upstream chamber 1313 will rapidlyfill with biological fluid from the bottom up. As upstream chamber 1313fills from the bottom up, the initial air in upstream chamber 1313 willbe displaced by the biological fluid filling upstream chamber 1313. Thedisplaced air will be forced through the BFFM, into vertical channels122 and 122 a and circular outlet channel 125, and then into outlet 1327all of BFFD 1400. The biological fluid in upstream chamber 1313 will bepressurized, with the pressure at the bottom of upstream chamber 1313being proportional to the distance from the top of the biological fluidin feed blood bag 98 to the bottom of upstream chamber 1313, and withthe pressure at the top of upstream chamber 1313 being proportional tothe distance from the top of the biological fluid in feed blood bag 98to the top of upstream chamber 1313. Hence the pressure at the top ofupstream chamber 1313 will be less than the pressure at the bottom offirst upstream chamber 1313. The positive pressure in upstream chamber1313 will cause the biological fluid to flow through first filterelement 815, and second filter element 816 over the entire surface areaof the first and second filter elements displacing the air within thepores of the first and second filter elements with biological fluid,thereby wetting the first and second filter elements from the upstreamside of first filter element 815 to the downstream side of second filterelement 816. The displaced air from upstream chamber 1313 and from thefirst and second filter elements will flow into third filter element817. Third filter element 817 preferably has an open pore size andstructure that allows flow through it in all directions. Therefore anyair or biological fluid that flows from the downstream surface of secondfilter element 816, will flow into third filter element 817 and then beuniformly distributed over the entire upstream surface of fourth filterelement 818, thereby utilizing fourth filter element 818 in the mostefficient way. As the first and second filter elements wet, the air thatwas initially in the pores of the first and second filter elements willbe displaced by biological fluid, and flow into the third filter element817. Because the pressure at the bottom of upstream chamber 1313 isgreater than the pressure at the top of upstream chamber 1313, the flowrate of biological fluid through the first and second filter elementswill be greater at the bottom of the first and second filter elementsthan at the top of the first and second filter elements. Therefore, thefirst and second filter elements will first become completely wettedfrom the upstream surface of the first filter element to downstreamsurface of the second filter element at the bottom of the second filterelement. The first and second filter elements will continue to wet withthe downstream surface of the second filter element wetting from thebottom to the top. The third filter element will also wet from thebottom to the top. When the liquid level in the third filter elementreaches the bottom of fourth filter element 818, the fourth filterelement will begin to wet from the bottom up. The first and secondfilter elements will continue to wet until all of the air in the firstand second filter elements has been purged. It is important that thehorizontal center line of first filter well 1311 is offset the requireddistance below the horizontal center line of second filter well 1311 aso that the top of first filter seal surface 1324 protrudes above thetop of second filter seal surface 1324 a no more than the distancerequired to create a compression seal at the top of the first filterwell between filter seal surface 107 of housing inlet half 101 a, andfirst filter seal surface 1324 of housing outlet half 1320, because airwill be trapped in the compression seal portion of the first, second,and third filter elements that lie above a horizontal line that istangent to the top of the perimeter of the second filter well. Thefourth filter element will wet from the bottom up, with the downstreamsurface of the fourth filter element first becoming wetted at the bottomof the downstream surface of the fourth filter element. If the width ofvertical channels 122 and 122 a is sufficiently small, and the depth ofvertical channels 122 and 122 a is sufficiently shallow, so that thecross-sectional flow area of the vertical channels 122 and 122 a issufficiently small, and if the distance between vertical channels 122and 122 a is sufficiently large, as described above in the descriptionof the second embodiment, the path of least resistance for continuedbiological fluid flow through the BFFM will be through the capillariesof the BFFM in both the horizontal and vertical directions and notthrough the vertical channels, because if the cross-sectional flow areaof the vertical channels is sufficiently small, the displaced airflowing into and through the vertical channels will create asufficiently high positive pressure in the vertical channels to preventbiological fluid from entering the vertical channels. The downstreamsurface of the BFFM (i.e. the downstream surface of the fourth filterelement) will therefore wet from the bottom up and the displaced airthat was within the BFFM will continue to flow into the verticalchannels, and into the circular outlet channel, and then into theoutlet. When the downstream surface of the BFFM has become wetted to thelevel of the upper part of circular outlet channel 125 where circularoutlet channel 125 begins to taper to a wider width, air flow throughthe lower part of circular outlet channel 125, and air flow through thetwo outermost vertical channels 122 a will stop because the downstreamsurface of the BFFM adjoining the lower part of the circular outletchannel and the two outermost vertical channels will be wetted.Therefore the pressure in the lower part of the circular outlet channeland the pressure in the two outermost vertical channels will decreaseallowing biological fluid to enter the lower part of the circular outletchannel and the two outermost vertical channels from the bottom up,thereby displacing the air that was in the lower part of the circularoutlet channel and the two outermost vertical channels. At the same timethe wetted level of the downstream surface of the BFFM will continue towet in the vertical direction, wetting the downstream surface of theBFFM adjoining the upper part of circular outlet channel 125. Becausethe cross-sectional flow area of the upper part of circular outletchannel 125 is not sufficiently small to create a positive pressure init due to the air flow through it, biological fluid will flow intocircular outlet channel 125 as the BFFM continues to wet in the verticaldirection above the lower part of the circular outlet channel. Thebiological fluid flowing into vertical channels 122 and 122 a, and intothe circular outlet channel 125 will flow into outlet 1327 of BFFD 1400and then into tubing 82 toward receiving blood bag 99. As biologicalfluid starts to flow into outlet 1327, the BFFM will continue to wetvertically. Hence the initial flow of biological fluid through the upperpart of circular outlet channel 125, and through outlet 1327, will be amixture of air and biological fluid so that the initial flow into tubing82 will consist of alternate segments of biological fluid and air. Asdescribed in the description of the second embodiment above, the amountof biological fluid that flows from outlet 1327 will be minimizedbecause of the design of the filter under drain structure, and becauseof the reduced surface area of the fourth filter element of the BFFM.

Referring to FIG. 1, FIG. 12, and FIG. 59, once all of the air has beenpurged from within BFFD 1400, biological fluid will continue to flowthrough the first fluid flow path from the inlet of BFFD 1400 to theoutlet of BFFD 1400, and then through tubing 82 into receiving blood bag99 until feed blood bag 98 is emptied of biological fluid. At this pointfeed blood bag 98 will be collapsed, effectively sealing the top oftubing 81, thereby preventing the flow of biological fluid in tubing 81.If receiving blood bag 99 is positioned at a level that is sufficientlylower than BFFD 1400, the pressure downstream of the BFFM and upstreamof outlet 1327 will be negative as described above in the description ofthe second embodiment. If BFFD 1400 is used in biological fluidfiltration system 1000 shown in FIG. 1, vent filtration device 30 andthree tube connector 50 will function as described in the description ofthe first embodiment above, and tubing 83, three tube connector 50,tubing 81 a, and upstream chamber 1313 of BFFD 1400 will drain asdescribed above. Vent inlet 178, vent inlet slot 177, and vent tubesocket 179 will not be used when BFFD 1400 replaces BFFD 100 inbiological fluid filtration system 1000. If BFFD 1400 is used inbiological fluid filtration system 2000 shown in FIG. 12, ventfiltration device 40 will be connected to vent inlet 178 of housinginlet half 101 a via tubing 85, and tubing 85 and upstream chamber 1313of BFFD 1400 will drain as described above in the description of thesecond embodiment.

Detailed Description of the Fifteenth Embodiment

A third embodiment of the biological fluid filtration system, and afifteenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 61 through FIG.74. Biological fluid filtration system 3000 shown in FIG. 61 containsfirst feed blood 98, second feed blood bag 98 a, first receiving bloodbag 99, and second receiving blood bag 99 a. Interposed between the feedblood bags and receiving blood bags is BFFD 1500. First length of tubing81 connects the outlet of first feed blood bag 98 to the first inlettube socket 106 of BFFD 1500. A second length of tubing 81 b connectsthe outlet of second feed blood bag 98 a to the second inlet tube socket106 a of BFFD 1500. A third length of tubing 82 connects first outlettube socket 1428 of BFFD 1500 to the inlet of first receiving blood bag99. A fourth length of tubing 82 a connects second outlet tube socket1428 a of BFFD 1500 to the inlet of second receiving blood bag 99 a. Afifth length of tubing 83 connects first vent tube socket 179 of BFFD1500 to first tube socket 1445 of vent filtration device 1440. A sixthlength of tubing 83 a connects second vent tube socket 179 a of BFFD1500 to second tube socket 1445 a of vent filtration device 1440.

Referring to FIG. 62, BFFD 1500 contains a rigid housing that includesfirst housing inlet half 101 a, second housing inlet half 101 aa, andhousing outlet half 1420. Preferably the housing inlet halves are bondedto the housing outlet half with an ultrasonic weld, but may be a heatbonded, a glue bonded, a solvent bonded, or bonded by any other type ofleak tight bond.

Referring to FIG. 62, first housing inlet half 101 a and second housinginlet half 101 aa are the same as housing inlet half 101 a shown in FIG.59, and described in the description of the fourteenth embodiment.

Referring to FIG. 62 through FIG. 68 housing outlet half 1420 contains asolid partition wall 1437 that divides BFFD 1500 into a first filtrationdevice with a first inlet and a first outlet on one side of the solidpartition wall, and a second filtration device with a second inlet and asecond outlet on the other side of the solid partition wall. On thefirst side of solid partition wall 1437 housing outlet half 1420contains first filter well 1411 bounded by inner side wall 1408 and byfirst filter seal surface 1424. Housing outlet half 1420 contains asecond filter well 1411 a on the opposite side of solid partition wall1437 bounded by inner side wall 1408 a and by second filter seal surface1424 a. Housing outlet half 1420 contains first circular outlet channel1425 and first outlet 1427 located on the first side of solid partitionwall 1437. The portion of first circular outlet channel 1425 thatadjoins and is in direct fluid flow communication with first outlet1427, has a cross-sectional flow area that is greater than thecross-sectional flow area of first outlet 1027 and is designated portion1425′. Referring to FIG. 68, portion 1425′ of first circular outletchannel 1425 is located near the top of first circular outlet channel1425 an to the right of vertical central axis CA1400V when viewed fromfirst filter well 1411. Housing outlet half 1420 also contains aplurality of open top closed bottom first vertical channels 1422 and1422 a located on the first side of solid partition wall 1437. The topend of each of the first vertical channels 1422 and 1422 a is in fluidflow communication with first circular outlet channel 1425. The upperpart of first circular outlet channel 1425 increases in width toaccommodate the flow of biological fluid from first vertical channels1422 and 1422 a. The width of the remainder of first circular outletchannel 1425 (i.e. the lower part of first circular outlet channel 1425)is approximately equal to the width of the first vertical channels. Thetwo outermost first vertical channels designated as first verticalchannels 1422 a adjoin first circular outlet channel 1425 where thewidth of first circular outlet channel 1425 is approximately equal tothe width of the first vertical channels. The first circular outletchannel and the first vertical channels combined, create a first filterunder drain structure, and are cut into first inner wall 1421 of solidpartition wall 1437, so that the inner surface of all of the firstchannels lies below first inner wall 1421, as shown in FIG. 65. Thecross sectional area the first circular outlet channel and of the firstvertical channels is defined by the inner surface of each channel and bythe downstream surface of the first BFFM. Housing outlet half 1420 alsocontains second circular outlet channel 1425 a and second outlet 1427 alocated on the second side of solid partition wall 1437. The portion ofsecond circular outlet channel 1425 a that adjoins and is in directfluid flow communication with second outlet 1427 a, has across-sectional flow area that is greater than the cross-sectional flowarea of second outlet 1027 a and is designated portion 1425′a. Referringto FIG. 68, portion 1425′a of second circular outlet channel 1425 a(shown as dotted lines) is located near the top of second circularoutlet channel 1425 a an to the left of vertical central axis CA1400V,when viewed from first filter well 1411. Housing outlet half 1420 alsocontains a plurality of open top closed bottom second vertical channels1422 b and 1422 c located on the second side of solid partition wall1437. The top end of each of the second vertical channels 1422 b and1422 c is in fluid flow communication with second circular outletchannel 1425 a. The upper part of second circular outlet channel 1425 aincreases in width to accommodate the flow of biological fluid fromsecond vertical channels 1422 b and 1422 c. The width of the remainderof second circular outlet channel 1425 a (i.e. the lower part of secondcircular outlet channel 1425 a) is approximately equal to the width ofthe second vertical channels. The two outermost second vertical channelsdesignated as second vertical channels 1422 c adjoin second circularoutlet channel 1425 a where the width of second circular outlet channel1425 a is approximately equal to the width of the second verticalchannels. The second circular outlet channel and the second verticalchannels combined, create a second filter under drain structure, thatare cut into second inner wall 1421 a of solid partition wall 1437, sothat the inner surface of all of the second channels lies below secondinner wall 1421 a, as shown in FIG. 67. The cross sectional area thesecond circular outlet channel and of the second vertical channels isdefined by the inner surface of each channel and by the downstreamsurface of the second BFFM. Solid partition wall 1437 provides a barrierbetween first circular outlet channel 1425 and second circular outletchannel 1425 a, and between first outlet 1427 and second outlet 1427 a.As shown in FIG. 65 and FIG. 66, the distance between first verticalchannels 1422 and 1422 a is much greater than the width of firstvertical channels 1422 and 1422 a, and the distance between firstvertical channels 1422 and 1422 a is also much greater than of the depthof first vertical channels 1422 and 1422 a. As shown in FIG. 67, thedistance between second vertical channels 1422 b and 1422 c is muchgreater than the width of second vertical channels 1422 b and 1422 c,and the distance between second vertical channels 1422 b and 1422 c isalso much greater than of the depth of second vertical channels 1422 band 1422 c. Because housing outlet half 1420 does not contain an openchamber or plenum downstream of the first BFFM or downstream of thesecond BFFM, hold up volume is minimized. FIG. 62 through FIG. 65 showthat first filter well 1411 is deeper than second filter well 1411 a.However the two filter well could be made to the same depth.

Referring to FIG. 62 through FIG. 65, BFFD 1500 contains a first BFFMand a second BFFM. The first BFFM is disposed in first filter well 1411,and the second BFFM is disposed in second filter well 1411 a. Referringto FIG. 62 through FIG. 64, the first BFFM contains four filterelements, first filter element 1415, second filter element 1416, thirdfilter element 1417, and fourth filter element 1418 comprised of threelayers of filter material of the same type. Any of the filter elementsmay contain one or more layers of the filter material of the same type.The first filter element has a pore size greater than the pore size ofthe second filter element, the fourth filter element has a pore sizesmaller than the pore size of the second filter element, while the thirdfilter element has a pore size greater than the pore size of the secondfilter element. Preferably the pore size of the third filter element isgreater than the pore size of the first and second filter elements. WhenBFFD 1500 is used to filter blood or blood product, first filter element1415 may be sized to remove gels from the blood or blood product, secondfilter element 1416 may be sized to remove microaggregates from theblood or blood product, fourth filter element 1418 may be sized toremove leukocytes from the blood or blood product, while the thirdfilter element 1417 is sized to act as a flow distribution layer.Because gels and microaggregates are large particles they may clumptogether thereby reducing the flow through the gel-microaggregate filterelements in the region of the clump. The flow distribution filterelement will distribute the effluent from the microaggregate filterelement evenly over the upstream surface of the leukocyte removinglayer, thereby allowing the leukocyte removing layer to be utilized mostefficiently. The outside diameter of first filter element 1415 issmaller than the inside diameter of inner side wall 1408 of housingoutlet half 1420 preventing first filter element 1415 from being sealedto BFFD 1500 with an interference fit between the perimeter surface 1415b of first filter element 1415 and inner side wall 1408 of housingoutlet half 1420. First filter element 1415 is sealed to the housing bycompressing the outer periphery of first filter element 1415 with filterseal surface 1407 of housing inlet half 101 a. Second filter element1416 and fourth filter element 1418 are sealed to the housing aninterference fit between the perimeter surface of each filter elementand inner side wall 1408 of housing outlet half 1420. Alternately boththe first and second filter elements could have outside diameters thatare smaller than the inside diameter of inner side wall 1408 of thehousing outlet half, thereby preventing both the first filter elementand the second filter element from being sealed to BFFD 1500 with aninterference fit between the perimeter surface of the filters and innerside wall 1498 of housing outlet half 1429. The outside diameter ofthird filter element 1417 is smaller than the inside diameter of innerside wall 1408 of housing outlet half 1420 preventing third filterelement 1417 from being sealed to BFFD 1500 with an interference fitbetween the perimeter surface of filter element 1417 and inner side wall1408 of housing outlet half 1420. Third filter element 1417 ispreferably a woven or non-woven screen filter, but could be any type ofopen pore size depth filter, or any other type of structure thatprovides for flow in all directions. The main purpose of filter element1417 is flow distribution therefore it has a large pore size, and ispreferably structured to allow flow through it in all directions. Inapplications where the blood or blood product is fresh and does notcontain gels, the first filter element may be a microaggregate removingfilter element, and the second filter element could be eliminated. Inthis case the third filter element may also be eliminated. Referring toFIG. 62 through FIG. 65, the second BFFM contains filter element 1471.The outside diameter of filter element 1471 is smaller than the insidediameter of inner side wall 1408 a of housing outlet half 1420preventing filter element 1471 from being sealed to BFFD 1500 with aninterference fit between the perimeter surface 1471 b of filter element1471 and inner side wall 1408 a of housing outlet half 1420. Filterelement 1471 is sealed to the housing by compressing the outer peripheryof filter element 1471 between filter seal surface 1407 a of housinginlet half 101 as and second filter seal surface 1424 a of housingoutlet half 1420. Any of the filter elements in the first filter wellcould also be bonded to the housing outlet half using a heat bond, anultrasonic bond, a glue bond, a solvent bond or any other type of leaktight bond, in place of, or in addition to, the use of perimeter sealsor compression seals. Likewise the filter element in the second filterwell could be bonded to the housing outlet half using a heat bond, anultrasonic bond, a glue bond, a solvent bond or any other type of leaktight bond, in place of, or in addition to, the use of a perimeter sealor compression seal. Second filter well 1411 a could be made as deep asfirst filter well 1411, thereby allowing the second filter well tocontain a second BFFM that is the same as the first BFFM contained inthe first filter well.

Referring to FIG. 62 through FIG. 68, a first fluid flow path is definedbetween first inlet 105 of BFFD 1500 and first outlet 1427 of BFFD 1500with the first BFFM interposed between first inlet 105 and first outlet1427, and across the first fluid flow path. The first fluid flow pathflows from first inlet 105, through first inlet slot 102, into firstupstream chamber first 1413, through the first BFFM, into first verticalchannels 1422 and 1422 a, into first circular outlet channel 1425, andthen into first outlet 1427. A second fluid flow path is defined betweensecond inlet 105 a of BFFD 1500 and second outlet 1427 a of BFFD 1500with the second BFFM interposed between second inlet 105 a and secondoutlet 1427 a, and across the second fluid flow path. The second fluidflow path flows from second inlet 105 a, through second inlet slot 102a, into second upstream chamber 1413 a, through the second BFFM, intosecond vertical channels 1422 b and 1422 c, into second circular outletchannel 1425 a, and then into second outlet 1427 a. The first fluid flowpath is independent of the second fluid flow path, and there is no crosstalk between the two. Solid partition wall 1437 is a barrier between thefirst fluid flow path and the second fluid flow path.

Referring to FIG. 69 through FIG. 71, and FIG. 73, vent filtrationdevice 1440 contains a housing comprised of housing cap 1441 and housingbody 1442. The housing contains a vent port 1446, a first system port1444, a second system port 1444 a, a first tube socket 1445, and asecond tube socket 1445 a. Housing body 1442 contains two filter supportstructures separated by solid partition wall 1459. The first filtersupport structure located on one side of solid partition wall 1459contains filter support ribs 1447 and is in fluid flow communicationwith first system port 1444. The second filter support structure locatedon the other side of solid partition wall 1459 contains filter supportribs 1447 a and is in fluid flow communication with second system port1444 a. Housing body 1442 also contains a filter well 1452 into whichvent filtration media 1443 is inserted. Vent filtration media 1443 issealed to filter seal surface 1450 of housing body 1442 along filterseal area 1449 shown cross-hatched in FIG. 69, thereby isolating thefirst filter support structure and the first system port from the secondfilter support structure and the second system port. The seal ispreferably a heat seal, but could be an ultrasonic seal, a glue seal, asolvent seal, or any other type of leak tight seal. Alternately ventfiltration media 1443 could be made of two separate vent filtrationmedia, with one sealed over the first filter support structure, and withthe other sealed over the second filter support structure. Seal surface1454 of housing cap 1441 is sealed to seal surface 1453 of housing body1442. A first vent fluid flow path is defined between common vent port1446 and first system port 1444, with the portion of vent filtrationmedia 1443 that is enclosed by the filter seal around the first filtersupport structure interposed between common vent port 1446 and firstsystem port 1444 and across the first vent fluid flow path. A secondvent fluid flow path is defined between common vent port 1446 and secondsystem port 1444 a, with the portion of vent filtration media 1443 thatis enclosed by the filter seal around the second filter supportstructure interposed between common vent port 1446 and second systemport 1444 a and across the second vent fluid flow path. The ventfiltration media 1443 is shown as a microporous filter media such as a0.2 μm microporous filter material, but may be any type of depth filtermedia, such as a non-woven depth filter material, a spun bound filtermaterial, a molded porous filter material or any other type of depthfilter material. The vent filtration media may be hydrophobic orhydrophilic. Preferably vent filtration device 1440 is located asufficient distance above inlet 105 and inlet 105 a of BFFD 1500 toprevent biological fluid in tubing 83 and tubing 83 a from contactingvent filtration media 1443 when biological fluid flows through BFFD1500. Vent filtration device 1440 may be located above the liquid levelin first feed blood bag 98 and second feed blood bag 98 a as shown inFIG. 61. Alternately housing cap 1441′ shown in FIG. 72 could replacehousing cap 1441 in vent filtration device 1440. Housing cap 1441′ isthe same as housing body 1442 with the exception that housing cap 1441′does not contain a filter well. When housing cap 1441′ is used toreplace housing cap 1441, vent filtration media 1443 could be sealed tovent filtration device 1440 by compressing vent filtration media 1443between seal surface 1451 of housing cap 1441′ and filter seal surface1450 of housing body 1442. When housing cap 1441′ is used to replacehousing cap 1441, a first vent fluid flow path is defined between firstvent port 1446′ and first system port 1444, with the portion of ventfiltration media 1443 that is enclosed by the filter seal around thefirst filter support structure interposed between first vent port 1446′and the first system port 1444 and across the first vent fluid flowpath. A second vent fluid flow path is defined between second vent port1446′a and second system port 1444 a, with the portion of ventfiltration media 1443 that is enclosed by the filter seal around thesecond filter support structure interposed between second vent port1446′a and second system port 1444 a and across the second vent fluidflow path. Because the filter seal in vent filtration device 1440isolates the first filter support structure and first system port fromthe second filter support structure and the second system port, thefirst vent fluid flow path is isolated from the second vent fluid flowpath.

Referring to FIG. 74 vent filtration device 1430 could replace ventfiltration device 1440. Vent filtration device 1430 contains a housingcomprised of housing cap 1431 and housing body 1432. The housingcontains a first vent port 1436, a second vent port 1436 a, a firstsystem port 1434, a second system port 1434 a, a first vent filtrationmedia 1433, and a second vent filtration media 1433 a. A first ventfluid flow path is defined between first vent port 1436 and first systemport 1434, with first vent filtration media 1433 interposed between thefirst vent port and the first system port and across the first ventfluid flow path. A second vent fluid flow path is defined between secondvent port 1436 a and second system port 1434 a, with second ventfiltration media 1433 a interposed between the second vent port and thesecond system port and across the second vent fluid flow path. The firstvent fluid flow path of vent filtration device 1430 is isolated from thesecond vent fluid flow path of vent filtration device 1430 by solidpartition wall 1439. The vent filtration media 1433 and 1433 a are shownas a depth filter media, such as a wad of cotton, a non-woven depthfilter material, a spun bound filter material, a molded porous filtermaterial or any other type of depth filter material. The vent filtrationmedia may be hydrophobic or hydrophilic. Preferably vent filtrationdevice 1430 is located above the liquid level in first feed blood bag 98and in second feed blood bag 98 a as shown in FIG. 61. Referring to FIG.61 and FIG. 74, when vent filtration device 1430 replaces ventfiltration device 1440 in biological fluid filtration system 3000, thetop end of tubing 83 would connect to first tube socket 1435 of ventfiltration device 1430, and the top end of tubing 83 a would connect tosecond tube socket 1435 a of vent filtration device 1430.

Referring to FIG. 61 through FIG. 68, and FIG. 73, biological fluidfiltration system 3000 may contain tubing 83, tubing 83 a, and ventfiltration device 1440. One end of tubing 83 is connected to first tubesocket 1445 of vent filtration device 1440 and the other end of tubing83 is connected to first vent tube socket 179 of BFFD 1500. One end oftubing 83 a is connected to second tube socket 1445 a of vent filtrationdevice 1440 and the other end of tubing 83 a is connected to second venttube socket 179 a of BFFD 1500. A third fluid flow path for biologicalfluid filtration system 3000 is defined from atmosphere to first ventinlet 178 of BFFD 1500. The third fluid flow path for biological fluidfiltration system 3000 flows from common vent port 1446 of ventfiltration device 1440, through the portion of vent filtration media1443 that is enclosed by the filter seal around the first filter supportstructure of vent filtration device 1440, through first system port 1444of vent filtration device 1440 through tubing 83, into first vent inlet178 of BFFD 1500, when tube clamp 94 is open. A fourth fluid flow pathfor biological fluid filtration system 3000 is defined from atmosphereto second vent inlet 178 a of BFFD 1500. The fourth fluid flow path forbiological fluid filtration system 3000 flows from common vent port 1446of vent filtration device 1440, through the portion of vent filtrationmedia 1443 that is enclosed by the filter seal around the second filtersupport structure of vent filtration device 1440, through second systemport 1444 a of vent filtration device 1440 through tubing 83 a, intosecond vent inlet 178 a of BFFD 1500, when tube clamp 94 a is open.Preferably vent filtration device 1440 is located above the liquid levelin first feed blood bag 98 and second feed blood bag 98 a, as shown inFIG. 61.

Referring to FIG. 61, biological fluid filtration system 3000 functionsas follows. The user will purchase the system with all components asshown in FIG. 61, less first feed blood bag 98 and second feed blood bag98 a. The user will connect tubing 81 to outlet 92 of first feed bloodbag 98 in a manner known in the art. The user will also connect tubing81 b to outlet 92 a of second feed blood bag 98 a in a manner known inthe art. First feed blood bag 98, second feed blood bag 98 a, and ventfiltration device 1440 may be hung from a blood bag pole known in theart, with first receiving blood bag 99 and second receiving blood bag 99a placed on a table top or the like, so that the various components ofthe system will be positioned as shown in FIG. 61. Tube clamps 95 and 95a should be closed before connecting tubing 81 to first feed blood bag98 and before connecting tubing 81 b to second feed blood bag 98 a.Before opening tube clamps 95 and 95 a to start the flow of biologicalfluid through the system, tube clamps 94, 94 a, 96, and 96 a should beopen.

Alternately the user will purchase the system with all components asshown in FIG. 61 including the first and second feed blood bags. In thiscase biological fluid filtration system 3000 may be part of a largersystem that contains a unit of fresh blood. The larger system would beplaced into a centrifuge where the platelets would be separated from theunit of fresh blood and then transferred into second feed blood bag 98a, and where the packed red blood cells would be separated from the unitof fresh blood and then transferred into first feed blood bag 98, usinga process known in the art.

Referring to FIG. 61 through FIG. 68, the first fluid flow path of BFFD1500 functions as follows. When tube clamp 95 is opened biological fluid(i.e. liquid) will flow from first feed blood bag 98, through tubing 81,into first inlet 105 of BFFD 1500, and then through first inlet slot 102of BFFD 1500, into first upstream chamber 1413 of BFFD 1500. Firstupstream chamber 1413 will rapidly fill with biological fluid from thebottom up. As first upstream chamber 1413 fills from the bottom up, theinitial air in first upstream chamber 1413 will be displaced by thebiological fluid filling first upstream chamber 1413. The displaced airwill be forced through the first BFFM, into first vertical channels 1422and 1422 a, into first circular outlet channel 1425, and then into firstoutlet 1427 all of BFFD 1500. The biological fluid in first upstreamchamber 1413 will be pressurized, with the pressure at the bottom offirst upstream chamber 1413 being proportional to the distance from thetop of the biological fluid in first feed blood bag 98 to the bottom offirst upstream chamber 1413, and with the pressure at the top of firstupstream chamber 1413 being proportional to the distance from the top ofthe biological fluid in first feed blood bag 98 to the top of firstupstream chamber 1413. Hence the pressure at the top of first upstreamchamber 1413 will be less than the pressure at the bottom of firstupstream chamber 1413. The positive pressure in first upstream chamber1413 will cause the biological fluid to flow through the first BFFM overthe entire surface area of the first BFFM and to displace the air withinthe pores of the first BFFM with biological fluid, thereby wetting thefirst BFFM from the upstream side of the first BFFM to the downstreamside of the first BFFM. As the first BFFM wets the air that wasinitially in the pores of the first BFFM will be displaced by biologicalfluid and flow into first vertical channels 1422 and 1422 a, and intofirst circular outlet channel 1425, and then into first outlet 1427 allof BFFD 1500, into tubing 82, and then into first receiving blood bag99. Because the pressure at the bottom of first upstream chamber 1413 isgreater than the pressure at the top of first upstream chamber 1413, theflow rate of biological fluid through the first BFFM will be greater atthe bottom of the first BFFM than at the top of the first BFFM.Therefore, the first BFFM will first become completely wetted from itsupstream surface to its downstream surface, at the bottom of the firstBFFM. If the width of first vertical channels 1422 and 1422 a issufficiently small, and the depth of first vertical channels 1422 and1422 a is sufficiently shallow, so that the cross-sectional flow area offirst vertical channels 1422 and 1422 a is sufficiently small, and ifthe distance between first vertical channels 1422 is sufficiently large,as described above, the path of least resistance for continuedbiological fluid flow through the first BFFM will be through thecapillaries of the first BFFM in both the horizontal and verticaldirections and not through the first vertical channels, because if thecross-sectional flow area of the first vertical channels is sufficientlysmall, the displaced air flowing into and through the first verticalchannels will create a sufficiently high positive pressure in the firstvertical channels to prevent biological fluid from entering the firstvertical channels. The downstream surface of the first BFFM willtherefore wet from the bottom up and the displaced air that was withinthe first BFFM will continue to flow into the first vertical channels,and into the first circular outlet channel, and then into the firstoutlet. When the downstream surface of the first BFFM has become wettedto the level of the upper part of first circular outlet channel 1425where first circular outlet channel 1425 begins to taper to a widerwidth, air flow through the lower part of first circular outlet channel1425, and air flow through the two outermost first vertical channels1422 a will stop because the downstream surface of the first BFFMadjoining the lower part of the first circular outlet channel and thetwo outermost first vertical channels will be wetted. Therefore thepressure in the lower part of the first circular outlet channel and thepressure in the two outermost first vertical channels will decreaseallowing biological fluid to enter the lower part of the first circularoutlet channel and the two outermost first vertical channels from thebottom up, thereby displacing the air that was in the lower part of thefirst circular outlet channel and the two outermost first verticalchannels. At the same time the wetted level of the downstream surface ofthe first BFFM will continue to wet in the vertical direction, wettingthe downstream surface of the first BFFM adjoining the upper part offirst circular outlet channel 1425. Because the cross-sectional flowarea of the upper part of first circular outlet channel 1425 is notsufficiently small to create a positive pressure in it due to the airflow through it, biological fluid will flow into first circular outletchannel 1425 as first BFFM continues to wet in the vertical directionabove the lower part of the first circular outlet channel. Thebiological fluid flowing into first vertical channels 1422 and 1422 a,and into the first circular outlet channel 1425 will flow into firstoutlet 1427 of BFFD 1500 and then into tubing 82 toward first receivingblood bag 99. As biological fluid starts to flow into first outlet 1427,first BFFM will continue to wet vertically. Hence the initial flow ofbiological fluid through the upper part of first circular outlet channel1425, and through first outlet 1427, will be a mixture of air andbiological fluid so that the initial flow into tubing 82 will consist ofalternate segments of biological fluid and air.

Referring to FIG. 61 through FIG. 64, when biological fluid starts toflow into tubing 82, the pressure P8 downstream of the first BFFM andupstream of first outlet 1427 (i.e. downstream of the first BFFM, butwithin BFFD 1500) will be determined by the following formula:P8=L7−p−L8

-   -   Δp is the pressure drop across the first BFFM due to biological        fluid flow through the first BFFM.    -   L7 is the distance between first outlet 1427 of BFFD 1500 and        the top of the biological fluid in first feed blood bag 98.    -   L8 is the height of biological fluid minus any air segments        downstream of first outlet 1427, in tubing 82.        Therefore the pressure P8 within BFFD 1500 and downstream of the        first BFFM will be greater than or equal to zero until L8=L7−Δp.        Because the upper part of first circular outlet channel 1425 is        located a sufficient distance above the horizontal center line        of BFFD 1500, all of the air will be purged from within the        first fluid flow path of BFFD 1500 before the pressure P8        becomes negative. As described above the pressure within first        upstream chamber 1413 of BFFD 1500 will be positive as long as        biological fluid is flowing into first upstream chamber 1413.        The purging of air from within the first fluid flow path BFFD        1500 is totally independent of whether or not the pressure        within BFFD 1500 downstream of the first BFFM becomes negative.

Referring to FIG. 61 through FIG. 65 and FIG. 73, once all of the airhas been purged from within the first fluid flow path of BFFD 1500,biological fluid will continue to flow through the first fluid flow pathfrom the first inlet of BFFD 1500 to the first outlet of BFFD 1500, andthen through tubing 82 into first receiving blood bag 99 until firstfeed blood bag 98 is emptied of biological fluid. At this point firstfeed blood bag 98 will be collapsed, effectively sealing the top oftubing 81, thereby preventing the flow of biological fluid in tubing 81.With flow through tubing 81 shut off as just described, air will nowflow through the third fluid flow path from common vent port 1446 ofvent filtration device 1440, through the portion of vent filtrationmedia 1443 that is enclosed by the filter seal around the first filtersupport structure of vent filtration device 1440, through first systemport 1444 of vent filtration device 1440 through tubing 83, into firstvent inlet 178, through first vent inlet slot 177, and then into firstupstream chamber 1413, thereby draining the biological fluid in firstupstream chamber 1413 of BFFD 1500. To complete the draining ofbiological fluid as just described, first receiving blood bag 99 must bepositioned a sufficient distance below outlet 1427 of BFFD 1500 tocreate a sufficiently negative pressure downstream of the first BFFM andupstream of outlet 1427 after all of the air has been purged from withinBFFD 1500 and tubing 82 is filled with biological fluid, to create asufficient pressure differential between the upstream surface and thedownstream surface of the first BFFM to drain first upstream chamber1413 to the bottom of first upstream chamber 1413, because as thebiological fluid level in first upstream chamber 1413 approaches thebottom of first upstream chamber 1413, the pressure on the bottom of thebiological fluid in first upstream 1413 will approach zero.

Referring to FIG. 61 through FIG. 68, when the filtration cycle throughthe first fluid flow path is complete as just described, the first BFFMwill remain wetted, first vertical channels 1422 and 1422 a, and firstcircular outlet channel 1425 will be filled with biological fluid, andtubing 82 will be filled with biological fluid. Because BFFD 1500 doesnot contain a plenum downstream of the first BFFM, the hold up volume ofbiological fluid within the first fluid flow path of BFFD 1500 will beminimized.

Referring to FIG. 61 through FIG. 68, the second fluid flow path of BFFD1500 functions as follows. When tube clamp 95 a is opened biologicalfluid (i.e. liquid) will flow from second feed blood bag 98 a, throughtubing 81 b, into second inlet 105 a of BFFD 1500, and then throughsecond inlet slot 102 a of BFFD 1500, into second upstream chamber 1413a of BFFD 1500. Second upstream chamber 1413 a will rapidly fill withbiological fluid from the bottom up. As second upstream chamber 1413 afills from the bottom up, the initial air in second upstream chamber1413 a will be displaced by the biological fluid filling second upstreamchamber 1413 a. The displaced air will be forced through the secondBFFM, into second vertical channels 1422 b and 1422 c, into secondcircular outlet channel 1425 a, and then into second outlet 1427 a allof BFFD 1500. The biological fluid in second upstream chamber 1413 awill be pressurized, with the pressure at the bottom of second upstreamchamber 1413 a being proportional to the distance from the top of thebiological fluid in second feed blood bag 98 a to the bottom of secondupstream chamber 1413 a, and with the pressure at the top of secondupstream chamber 1413 a being proportional to the distance from the topof the biological fluid in second feed blood bag 98 a to the top ofsecond upstream chamber 1413 a. Hence the pressure at the top of secondupstream chamber 1413 a will be less than the pressure at the bottom ofsecond upstream chamber 1413 a. The positive pressure in second upstreamchamber 1413 a will cause the biological fluid to flow through thesecond BFFM over the entire surface area of the second BFFM and todisplace the air within the pores of the second BFFM with biologicalfluid, thereby wetting the second BFFM from the upstream side of thesecond BFFM to the downstream side of the second BFFM. As the secondBFFM wets the air that was initially in the pores of the second BFFMwill be displaced by biological fluid and flow into second verticalchannels 1422 b and 1422 c, and into second circular outlet channel 1425a, and then into second outlet 1427 a all of BFFD 1500, into tubing 82a, and then into second receiving blood bag 99 a. Because the pressureat the bottom of second upstream chamber 1413 a is greater than thepressure at the top of second upstream chamber 1413 a, the flow rate ofbiological fluid through the second BFFM will be greater at the bottomof the second BFFM than at the top of the second BFFM. Therefore, thesecond BFFM will first become completely wetted from its upstreamsurface to its downstream surface, at the bottom of the second BFFM. Ifthe width of second vertical channels 1422 b and 1422 c is sufficientlysmall, and the depth of second vertical channels 1422 b and 1422 c issufficiently shallow, so that the cross-sectional flow area of secondvertical channels 1422 b and 1422 c is sufficiently small, and if thedistance between second vertical channels 1422 b and 1422 c issufficiently large, as described above, the path of least resistance forcontinued biological fluid flow through the second BFFM will be throughthe capillaries of the second BFFM in both the horizontal and verticaldirections and not through the second vertical channels, because if thecross-sectional flow area of the second vertical channels issufficiently small, the displaced air flowing into and through thesecond vertical channels will create a sufficiently high positivepressure in the second vertical channels to prevent biological fluidfrom entering the second vertical channels. The downstream surface ofthe second BFFM will therefore wet from the bottom up and the displacedair that was within the second BFFM will continue to flow into thesecond vertical channels, and into the second circular outlet channel,and then into the second outlet. When the downstream surface of thesecond BFFM has become wetted to the level of the upper part of secondcircular outlet channel 1425 a where second circular outlet channel 1425a begins to taper to a wider width, air flow through the lower part ofsecond circular outlet channel 1425 a, and air flow through the twooutermost second vertical channels 1422 c will stop because thedownstream surface of the second BFFM adjoining the lower part of thesecond circular outlet channel and the two outermost second verticalchannels will be wetted. Therefore the pressure in the lower part of thesecond circular outlet channel and the pressure in the two outermostsecond vertical channels will decrease allowing biological fluid toenter the lower part of the second circular outlet channel and the twooutermost second vertical channels from the bottom up, therebydisplacing the air that was in the lower part of the second circularoutlet channel and the two outermost second vertical channels. At thesame time the wetted level of the downstream surface of the second BFFMwill continue to wet in the vertical direction, wetting the downstreamsurface of the second BFFM adjoining the upper part of second circularoutlet channel 1425 a. Because the cross-sectional flow area of theupper part of second circular outlet channel 1425 a is not sufficientlysmall to create a positive pressure in it due to the air flow throughit, biological fluid will flow into second circular outlet channel 1425a as the second BFFM continues to wet in the vertical direction abovethe lower part of the second circular outlet channel. The biologicalfluid flowing into second vertical channels 1422 b and 1422 c, and intothe second circular outlet channel 1425 a will flow into second outlet1427 a of BFFD 1500 and then into tubing 82 a toward second receivingblood bag 99 a. As biological fluid starts to flow into second outlet1427 a, second BFFM will continue to wet vertically. Hence the initialflow of biological fluid through the upper part of second circularoutlet channel 1425 a, and through second outlet 1427 a, will be amixture of air and biological fluid so that the initial flow into tubing82 a will consist of alternate segments of biological fluid and air.

Referring to FIG. 61 through FIG. 64, when biological fluid starts toflow into tubing 82 a, the pressure P9 downstream of the second BFFM andupstream of second outlet 1427 a (i.e. downstream of the second BFFM,but within BFFD 1500) will be determined by the following formula:P9=L9−Δp−L10

-   -   Δp is the pressure drop across the second BFFM due to biological        fluid flow through the second BFFM.    -   L9 is the distance between second outlet 1427 a of BFFD 1500 and        the top of the biological fluid in second feed blood bag 98 a.    -   L10 is the height of biological fluid minus any air segments        downstream of second outlet 1427 a, in tubing 82 a.        Therefore the pressure P9 within BFFD 1500 and downstream of the        second BFFM will be greater than or equal to zero until        L10=L9−Δp. Because the upper part of second circular outlet        channel 1425 a is located a sufficient distance above the        horizontal center line of BFFD 1500, all of the air will be        purged from within the second fluid flow path of BFFD 1500        before the pressure P9 becomes negative. As described above the        pressure within second upstream chamber 1413 a of BFFD 1500 will        be positive as long as biological fluid is flowing into second        upstream chamber 1413 a. The purging of air from within the        second fluid flow path of BFFD 1500 is totally independent of        whether or not the pressure within BFFD 1500 downstream of the        second BFFM becomes negative.

Referring to FIG. 61 through FIG. 65 and FIG. 73, once all of the airhas been purged from within the second fluid flow path of BFFD 1500,biological fluid will continue to flow through the second fluid flowpath from the second inlet of BFFD 1500 to the second outlet of BFFD1500, and then through tubing 82 a into second receiving blood bag 99 auntil second feed blood bag 98 a is emptied of biological fluid. At thispoint second feed blood bag 98 a will be collapsed, effectively sealingthe top of tubing 81 b, thereby preventing the flow of biological fluidin tubing 81 b. With flow through tubing 81 b shut off as justdescribed, air will now flow through the fourth fluid flow path fromcommon vent port 1446 of vent filtration device 1440, through theportion of vent filtration media 1443 that is enclosed by the filterseal around the second filter support structure of vent filtrationdevice 1440, through second system port 1444 a of vent filtration device1440 through tubing 83 a, into second vent inlet 178 a, through secondvent inlet slot 177 a, and then into second upstream chamber 1413 a,thereby draining the biological fluid in second upstream chamber 1413 aof BFFD 1500. To complete the draining of biological fluid as justdescribed, second receiving blood bag 99 a must be positioned asufficient distance below second outlet 1427 a of BFFD 1500 to create asufficiently negative pressure downstream of the second BFFM andupstream of second outlet 1427 after all of the air has been purged fromwithin BFFD 1500 and tubing 82 a is filled with biological fluid, tocreate a sufficient pressure differential between the upstream surfaceand the downstream surface of the second BFFM to drain second upstreamchamber 1413 a to the bottom of second upstream chamber 1413 a, becauseas the biological fluid level in second upstream chamber 1413 aapproaches the bottom of second upstream chamber 1413 a, the pressure onthe bottom of the biological fluid in second upstream 1413 a willapproach zero.

Referring to FIG. 61 through FIG. 68, when the filtration cycle throughthe second fluid flow path is complete as just described, the secondBFFM will remain wetted, second vertical channels 1422 b and 1422 c, andsecond circular outlet channel 1425 a will be filled with biologicalfluid, and tubing 82 a will be filled with biological fluid. BecauseBFFD 1500 does not contain a plenum downstream of the second BFFM, thehold up volume of biological fluid within the second fluid flow path ofBFFD 1500 will be minimized.

Once the filtration cycle through the first and second fluid flow pathsof BFFD 1500 is complete as just described, the user will close tubeclamp 96 and tube clamp 96 a, and then cut and seal tubing 82 above tubeclamp 96, and then cut and seal tubing 82 a above tube clamp 96 a, andthen discard BFFD 1500 and the remaining components attached to it in asafe manner.

As can be seen from the above description, the flow of biological fluidthrough first fluid flow path of BFFD 1500 is completely independent ofthe flow of biological fluid through second fluid flow path of BFFD1500, and that solid partition wall 1437 of housing outlet half 1420isolates the first fluid flow path from the second fluid flow path.

Detailed Description of the Sixteenth Embodiment

A sixteenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 75 through FIG.79. BFFD 1600 may be used in place of BFFD 1500 in biological fluidfiltration system 3000 shown in FIG. 61.

Referring to FIG. 75 through FIG. 77, BFFD 1600 contains a rigid housingthat includes housing inlet half 201′, housing inlet half 201′a, andhousing outlet half 1520. Housing inlet half's 201′, and 201′a are sameas housing inlet half 201 of the third embodiment (shown in FIG. 18)with the exception that inner side wall 208 is shorter. Inner side wall208 of housing inlet half 201′ and inner side wall 208 of housing inlethalf 201′a are bonded to outer side wall 1529 of housing outlet half1520. The bond is preferably an ultrasonic weld but may be a heat bond,a glue bond, a solvent bond, or any other type of leak tight bond.

Referring to FIG. 20, FIG. 21, and FIG. 75 through FIG. 77, BFFD 1600contains first flexible diaphragm 260 and second flexible diaphragm 260a. First flexible diaphragm 260 and second flexible diaphragm 260 ashown in FIG. 75 through FIG. 77 are the same as flexible diaphragm 260shown in FIG. 20 and FIG. 21 and described in the third embodiment ofthe present invention.

Referring to FIG. 75 through FIG. 79 housing outlet half 1520 contains asolid partition wall 1537 that divides BFFD 1600 into a first filtrationdevice with a first inlet and a first outlet on one side of the solidpartition wall, and a second filtration device with a second inlet and asecond outlet on the other side of the solid partition wall. On thefirst side of solid partition wall 1537 housing outlet half 1520contains first filter well 1511 bounded by inner side wall 1408 and byfirst filter seal surface 1424. Housing outlet half 1520 contains asecond filter well 1511 a on the opposite side of solid partition wall1537 bounded by inner side wall 1508 a and by second filter seal surface1524 a. Circular outlet channel 1425 and vertical channels 1422 and 1422a of housing outlet half 1520 combined, create a first filter underdrain structure, cut into first inner wall 1421 of solid partition wall1537 of housing outlet half 1520, that is the same as the first filterunder drain structure of housing outlet half 1420 of the fifteenthembodiment. First outlet 1427 of housing outlet half 1520 is also thesame as first outlet 1427 of housing outlet half 1420. The upper part offirst filter well 1511 contains seal ring counter bore 1526. Thereference numbers that were used to designate features of housing outlethalf 1420 of the fifteenth embodiment are used to designate identicalfeatures of housing outlet half 1520 of the sixteenth embodiment.

Referring to FIG. 75 through FIG. 79, the second filter well 1511 a ofhousing outlet half 1520 contains an open chamber or plenum 1530 definedby second inner wall 1521 a, by inner side wall 1508 b, and by a planethat goes through second filter seal surface 1524 a. Vertical filtersupport ribs 1522 a protrude from second inner wall 1521 a, with the topsurface of vertical filter support ribs lying in a plane that goesthrough second filter seal surface 1524 a. Plenum 1530 may be taperedlike plenum 830 shown in FIG. 40. Second outlet 1527 a is located nearthe top of plenum 1530. Slot 1525 a cut into second inner wall 1521 a isin fluid flow communication with second outlet 1527 a. Vertical filtersupport ribs 1522 a create a second filter under drain structure.

Referring to FIG. 75 through FIG. 79, BFFD 1600 contains a first BFFMand a second BFFM. The first BFFM is disposed in first filter well 1511,and the second BFFM is disposed in second filter well 1511 a. The firstBFFM of BFFD 1600 is the same as the first BFFM of BFFD 1500 describedin the fifteenth embodiment above. First filter element 1415 of BFFD1600 is sealed to the housing by compressing the outer periphery offirst filter element 1415 with filter seal ring 1560. Like the secondBFFM of BFFD 1500, the second BFFM of BFFD 1600 contains one filterelement 1571. Filter element 1571 is bonded to second filter sealsurface 1524 a of housing outlet half 1520 with bond 1573. The bond canbe a heat seal, an ultrasonic seal, a glue seal, a solvent seal, or anyother type of leak tight seal. Filter element 1571 could be a depthfilter, or it could be a microporous filter.

Referring to FIG. 75 through FIG. 79, a first fluid flow path is definedbetween first inlet 205 of BFFD 1600 and first outlet 1427 of BFFD 1600with the first BFFM interposed between first inlet 205 and first outlet1427, and across the first fluid flow path. The first fluid flow pathflows from first inlet 205, into first upstream chamber first 1513,through the first BFFM, into vertical channels 1422 and 1422 a, intocircular outlet channel 1425, and then into first outlet 1427. A secondfluid flow path is defined between second inlet 205 a of BFFD 1600 andsecond outlet 1527 a of BFFD 1600 with the second BFFM interposedbetween second inlet 205 a and second outlet 1527 a, and across thesecond fluid flow path. The second fluid flow path flows from secondinlet 205 a, into second upstream chamber 1513 a, through the secondBFFM, into plenum 1530 downstream of the second BFFM, into slot 1525 a,and then into second outlet 1527 a. The first fluid flow path isindependent of the second fluid flow path, and there is no cross talkbetween the two. Solid partition wall 1537 is a barrier between thefirst fluid flow path and the second fluid flow path.

Referring to FIG. 61, BFFD 1600 could replace BFFD 1500 in biologicalfluid filtration system 3000, in which case biological fluid filtrationsystem 3000 would function as follows. When BFFD 1600 replaces BFFD 1500vent filtration device 1440, tubing 83, and tubing 83 a will beeliminated. The outlet end of tubing 81 will be connected to inlet tubesocket 206 of BFFD 1600, and the outlet end of tubing 81 b will beconnected to inlet tube socket 206 a of BFFD 1600. The user willpurchase the system with all components as shown in FIG. 61, less ventfiltration device 1440, tubing 83, tubing 83 a, first feed blood bag 98and second feed blood bag 98 a. The user will connect tubing 81 tooutlet 92 of first feed blood bag 98 in a manner known in the art. Theuser will also connect tubing 81 b to outlet 92 a of second feed bloodbag 98 a in a manner known in the art. First feed blood bag 98 andsecond feed blood bag 98 a may be hung from a blood bag pole known inthe art, with first receiving blood bag 99 and second receiving bloodbag 99 a placed on a table top or the like, so that the variouscomponents of the system will be positioned as shown in FIG. 61. Tubeclamps 95 and 95 a should be closed before connecting tubing 81 to firstfeed blood bag 98 and before connecting tubing 81 b to second feed bloodbag 98 a. Before opening tube clamps 95 and 95 a to start the flow ofbiological fluid through the system, tube clamps 96, and 96 a should beopen.

Alternately the user will purchase the system with all components asjust described in the previous paragraph, including the first and secondfeed blood bags. In this case biological fluid filtration system 3000may be part of a larger system that contains a unit of fresh blood. Thelarger system would be placed into a centrifuge where the plateletswould be separated from the unit of fresh blood and then transferredinto second feed blood bag 98 a, and where the packed red blood cellswould be separated from the unit of fresh blood and then transferredinto first feed blood bag 98, using a process known in the art.

Referring to FIG. 75 through FIG. 79, the first fluid flow path of BFFD1600 functions as follows. When tube clamp 95 is opened biological fluid(i.e. liquid) will flow from first feed blood bag 98, through tubing 81,into first inlet 205 of BFFD 1600, and then into first upstream chamber1513 of BFFD 1600. First upstream chamber 1513 will rapidly fill withbiological fluid from the bottom up. Because first circular outletchannel 1425, and first vertical channels 1422 and 1422 a, and firstoutlet 1427 of housing outlet half 1520 of BFFD 1600 are identical tothe corresponding features of BFFD 1500, the first fluid flow path ofBFFD 1600 will fill and purge air as described in the description of thefirst fluid flow path for BFFD 1500 in the description of the fifteenthembodiment.

Referring to FIG. 18, FIG. 20, FIG. 21, FIG. 61, and FIG. 75 throughFIG. 79, once all of the air has been purged from the first fluid flowpath within BFFD 1600, biological fluid will continue to flow throughthe first fluid flow path from first inlet 205 of BFFD 1600 to firstoutlet 1427 of BFFD 1600, and then through tubing 82 into firstreceiving blood bag 99 until first feed blood bag 98 is emptied ofbiological fluid. At this point first feed blood bag 98 will becollapsed, effectively sealing the top of tubing 81, thereby preventingthe flow of biological fluid in tubing 81. If first receiving blood bag99 is positioned at a level that is sufficiently lower than BFFD 1600,the pressure downstream of the first BFFM and upstream of first outlet1427 will be negative as described above. Once first feed blood bag 98collapses and biological fluid flow through the first fluid flow pathstops the differential pressure across the first BFFM will become zero,hence the pressure in upstream chamber 1513 will become negative. Thepressure on upstream surface 266 of first flexible diaphragm 260 will beatmospheric because hole 271 of housing inlet half 201′ is open toatmosphere. With atmospheric pressure on the outer surface 266 of firstflexible diaphragm 260, the negative pressure within first upstreamchamber 1513 will cause first flexible diaphragm 260 to collapse ontothe upstream surface of the first BFFM, thereby forcing the biologicalfluid in first upstream chamber 1513 through the first BFFM, into thevertical channels and the circular outlet channel, into outlet 1427,into tubing 82, and then into first receiving blood bag 99.

Referring to FIG. 75 through FIG. 78, when the filtration cycle throughthe first fluid flow path of BFFD 1600 is complete as just described,the first BFFM will remain wetted, vertical channels 1422 and 1422 a,and circular outlet channel 1425 will be filled with biological fluid,and tubing 82 will be filled with biological fluid. Because BFFD 1600does not contain a plenum downstream of the first BFFM, the hold upvolume of biological fluid within the first fluid flow path of BFFD 1500will be minimized.

Referring to FIG. 61 and FIG. 75 through FIG. 77, and FIG. 79, thesecond fluid flow path of BFFD 1600 functions as follows. When tubeclamp 95 a is opened biological fluid (i.e. liquid) will flow fromsecond feed blood bag 98 a. Biological fluid will flow into inlet 205 a,into second upstream chamber 1513 a, of BFFD 1600. Second upstreamchamber 1513 a will rapidly fill with biological fluid from the bottomup. As second upstream chamber 1513 a fills from the bottom up, theinitial air in second upstream chamber 1513 a will be displaced by thebiological fluid filling second upstream chamber 1513 a. The displacedair will be forced through the second BFFM, into plenum 1530, into slot1525 a, and then into second outlet 1527 a all of BFFD 1600. Thebiological fluid in second upstream chamber 1513 a will be pressurized,with the pressure at the bottom of second upstream chamber 1513 a beingproportional to the distance from the top of the biological fluid insecond feed blood bag 98 a to the bottom of second upstream chamber 1513a, and with the pressure at the top of second upstream chamber 1513 abeing proportional to the distance from the top of the biological fluidin second feed blood bag 98 a to the top of second upstream chamber 1513a. Hence the pressure at the top of second upstream chamber 1513 a willbe less than the pressure at the bottom of second upstream chamber 1513a. The positive pressure in second upstream chamber 1513 a will causethe biological fluid to flow through the second BFFM over the entiresurface area of the second BFFM and to displace the air within the poresof the second BFFM with biological fluid, thereby wetting second BFFMfrom the upstream side of second BFFM to the downstream side of thesecond BFFM. As the second BFFM wets the air that was initially in thepores of second BFFM will be displaced by biological fluid and flow intoplenum 1530, into slot 1525 a, and then into outlet 1527 a, into tubing82 a, into second receiving blood bag 99 a. Because the pressure at thebottom of second upstream chamber 1513 a is greater than the pressure atthe top of second upstream chamber 1513 a, the flow rate of biologicalfluid through the second BFFM will be greater at the bottom of thesecond BFFM than at the top of the second BFFM. Therefore, the secondBFFM will first become completely wetted from the upstream surface ofthe second BFFM to the downstream surface of the second BFFM at thebottom of second BFFM. Once the bottom of the downstream surface of thesecond BFFM has been wetted, the remainder of the downstream surface ofthe second BFFM will continue to wet from the bottom up, and biologicalfluid will start to flow from the bottom of the second BFFM, into plenum1530. The plenum will fill from the bottom up forcing the air above theliquid level in the plenum into slot 1525 a, into second outlet 1527 a,into tubing 82 a, and then into second receiving blood bag 99 a. Theplenum will fill with biological fluid before all of the air has beenpurged from the upper portion of the second BFFM. The remaining air inthe un-wetted upper portion of the second BFFM will be displaced bybiological fluid and forced into the plenum, where it will bubble to thetop of the plenum due to the buoyancy of air in the biological fluid,and then be forced into outlet 1527 a, into tubing 82 a, and then intosecond receiving blood bag 99 a by the flow of biological fluid. Hencethe initial flow of biological fluid through outlet 1527 a, into tubing82 a will be a mixture of air and biological fluid, so that the initialflow into tubing 82 a will consist of alternate segments of biologicalfluid and air.

Referring to FIG. 18, FIG. 20, FIG. 21, FIG. 61, FIG. 75 through FIG.77, and FIG. 79, once all of the air has been purged from the secondfluid flow path within BFFD 1600, biological fluid will continue to flowthrough the second fluid flow path from second inlet 205 a of BFFD 1600to second outlet 1527 a of BFFD 1600, and then through tubing 82 a intosecond receiving blood bag 99 a until second feed blood bag 98 a isemptied of biological fluid. At this point second feed blood bag 98 awill be collapsed, effectively sealing the top of tubing 81 b, therebypreventing the flow of biological fluid in tubing 81 b. If secondreceiving blood bag 99 a is positioned at a level that is sufficientlylower than BFFD 1600, the pressure downstream of the second BFFM andupstream of second outlet 1527 a will be negative as described above.Once second feed blood bag 98 a collapses and biological fluid flowthrough the second fluid flow path stops the differential pressureacross the second BFFM will become zero, hence the pressure in secondupstream chamber 1513 a will become negative. The pressure on upstreamsurface 266 of second flexible diaphragm 260 a will be atmosphericbecause hole 271 a of housing inlet half 201′a is open to atmosphere.With atmospheric pressure on the outer surface 266 of second flexiblediaphragm 260 a, the negative pressure within second upstream chamber1513 a will cause second flexible diaphragm 260 a to collapse onto theupstream surface of the second BFFM, thereby forcing the biologicalfluid in second upstream chamber 1513 a through the second BFFM, intoplenum 1530, into second outlet 1527 a, into tubing 82 a, and then intosecond receiving blood bag 99 a.

Once the filtration cycle through the first and second fluid flow pathsof BFFD 1600 is complete as just described, the user will close tubeclamp 96 and tube clamp 96 a, and then cut and seal tubing 82 above tubeclamp 96, and then cut and seal tubing 82 a above tube clamp 96 a, andthen discard BFFD 1600 and the remaining components attached to it in asafe manner.

As can be seen from the above description, the flow of biological fluidthrough first fluid flow path of BFFD 1600 is completely independent ofthe flow of biological fluid through second fluid flow path of BFFD1600, and that solid partition wall 1537 of housing outlet half 1520isolates the first fluid flow path from the second fluid flow path.

Detailed Description of the Seventeenth Embodiment

A seventeenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 93 through FIG.97. BFFD 1900 may be used in place of BFFD 1500 in biological fluidfiltration system 3000 shown in FIG. 61.

Referring to FIG. 94, BFFD 1900 contains a rigid housing that includesfirst housing inlet half 1901, second housing inlet half 1901 a, andhousing outlet half 1920. Preferably the housing inlet halves are bondedto the housing outlet half with an ultrasonic weld, but may be a heatbonded, a glue bonded, a solvent bonded, or bonded by any other type ofleak tight bond.

Referring to FIGS. 94 through 97, first housing inlet half 1901 andsecond housing inlet half 1901 a are the same as housing inlet half 901shown in FIG. 48, with the following exceptions. Housing inlet half 1901and 1901 a do not contain circular rib 989 or slot 904 a, and the outerboundary of wall 1991 of housing inlet halves 1901 and 1901 a is thesame as the outer boundary of wall 1992 of housing outlet half 1920 asshown in FIGS. 94 and 95. Alternately housing inlet halves 1901 and 1901a could contain circular rib 989 and slot 904 a shown in FIG. 48, andseal rings 1950 and 1950 a could be eliminated. Housing inlet half 1901is bonded to seal surface 1929 of housing outlet half 1920 along weldcenterline WCL1971 shown in FIG. 96. Similarly housing inlet half 1901 ais bonded to seal surface 1929 a of housing outlet half 1920 along asimilar weld centerline.

Referring to FIG. 93 through FIG. 97 housing outlet half 1920 contains asolid partition wall 1937 that divides BFFD 1900 into a first filtrationdevice with a first inlet and a first outlet on one side of the solidpartition wall, and a second filtration device with a second inlet and asecond outlet on the other side of the solid partition wall. On thefirst side of solid partition wall 1937 housing outlet half 1920contains first filter well 1911 bounded by inner side wall 1908 and byfirst filter seal surface 1924, and second filter well 1911 a bounded byinner side wall 1908 a and by second filter seal surface 1924 a. Firstfilter well 1911 has a larger diameter than second filter well 1911 a.The horizontal center line of the first filter well is offset below thehorizontal center line of the second filter well so that the top ofinner side wall 1908 is tangent to the top of inner side wall 1908 a.Housing outlet half 1020 contains a third filter well and a fourthfilter well on the opposite side of solid partition wall 1937 that aremirror images of the first filter well and the second filter wellrespectively, mirrored about a plane that goes through the center of thesolid partition wall. Housing outlet half 1920 contains first arc outletchannel 1925 and first outlet 1927. First arc outlet channel 1925 is indirect fluid flow communication with outlet 1927, and the portion offirst arc outlet channel 1925 that adjoins outlet 1927 has across-sectional flow area that is greater than the cross-sectional flowarea of outlet 1927. Housing outlet half 1920 also contains a pluralityof open top closed bottom first vertical channels 1922 a and 1922. Thetop end of each of the first vertical channels 1922 a and 1922 is influid flow communication with first arc outlet channel 1925. The firstvertical channels are shown non-tapered, but could be tapered in widthand in depth. First arc outlet channel 1925 is sufficiently wide anddeep to accommodate the flow of biological fluid from first verticalchannels 1922 a and 1922. The first arc outlet channel and the firstvertical channels combined, create a first filter under drain structure,and are cut into first inner wall 1921 of solid partition wall 1937, sothat the inner surface of all of the first channels lies below firstinner wall 1921, as shown in FIG. 93. The cross sectional area the firstarc outlet channel and of the first vertical channels is defined by theinner surface of each channel and by the downstream surface of the firstBFFM. Housing outlet half 1920 contains a second arc outlet channel 1925a and a plurality of open top closed bottom second vertical channels1922 b and 1922 c on the second side of solid partition wall 1937.Vertical channels 1922 b and 1922 c are in fluid flow communication withsecond arc outlet channel 1925 a, and cut into second inner wall 1921 aof solid partition wall 1037. The second arc outlet channel and secondvertical channels create a second filter under drain structure shown inFIG. 97. FIG. 96 is a front view of housing outlet half 1920 showing thefirst filter under drain structure. FIG. 97 is a back view of housingoutlet half 1920 showing the second filter under drain structure. Theback view shown in FIG. 97 is obtained by rotating housing outlet half1920 shown in FIG. 96, 180° about central axis CL1970. Hence whenlooking from the front, first arc outlet channel 1925 sweeps counterclockwise from approximately 2 o'clock to approximately 6:30 o'clock,with the arc having an included angle substantially greater than 180°(i.e. substantially greater than a semi-circle), with the outlet portionof first arc outlet channel in direct fluid flow communication withfirst outlet 1927, which is located to the left of central axis CL1970when looking at the front of housing outlet half 1920. Similarly whenlooking from the front, second arc outlet channel 1925 a sweepsclockwise from approximately 10 o'clock to approximately 5:30 o'clock,with the arc having an included angle substantially greater than 180°(i.e. substantially greater than a semi-circle), with the outlet portionof second arc outlet channel in direct fluid flow communication withsecond outlet 1927 a (shown as dotted lines in FIG. 97), which islocated to the right of central axis CL1970 when looking at the front ofhousing outlet half 1920. As shown in FIG. 93 and FIG. 96, the distancebetween first vertical channels 1922 a and 1922 is much greater than thewidth of first vertical channels 1922 a and 1922, and the distancebetween first vertical channels 1922 a and 1922 is also much greaterthan of the depth of first vertical channels 1922 a and 1922. Referringto FIG. 96, the first vertical channels to the right of the outletportion of first arc outlet channel 1925 may be longer than those to theleft of the outlet portion of first arc outlet channel 1925 tocompensate for the lack of an outlet channel below these verticalchannels. Similarly referring to FIG. 97, the second vertical channelsto the right of the outlet portion of second arc outlet channel 1925 amay be longer than those to the left of the outlet portion of second arcoutlet channel 1925 a to compensate for the lack of an outlet channelbelow these vertical channels. Because housing outlet half 1920 does notcontain an open chamber or plenum downstream of the first BFFM ordownstream of the second BFFM, hold up volume is minimized. Housingoutlet half 1920 also contains first inlet 1905, first vent inlet 1978,first cross port 1902, and first inlet slot 1988. Housing outlet half1920 also contains second inlet 1905 a, second vent inlet 1978 a, secondcross port 1902 a, and second inlet slot 1988 a. Solid partition wall1937 isolates the first cross port from the second cross port. Firstinlet 1905 and first vent inlet 1978 are in fluid flow communicationwith first upstream chamber 1913 via first cross port 1902, and firstinlet slot 1988. Second inlet 1905 a and second vent inlet 1978 a are influid flow communication with second upstream chamber 1913 a via secondcross port 1902 a, and second inlet slot 1988 a. The upper part of firstfilter well 1911 contains a first seal ring counter bore bounded byinner side wall 1908 b, and by surface 1960. The upper part of thirdfilter well 1911 b contains a second seal ring counter bore that is amirror image of the first seal ring counter bore, mirrored about a planethat goes through the center of the solid partition wall.

Referring to FIG. 94, BFFD 1900 contains a first BFFM and a second BFFM.The first BFFM is disposed in first filter well 1911 and second filterwell 1911 a on the first side of solid partition wall 1937, and thesecond BFFM is disposed in third filter well 1911 b and fourth filterwell 1911 c on the second side of solid partition wall 1937. The BFFM'sare asymmetrical in that first BFFM contains five filter elements, andthe second BFFM each contains three filter elements. The first BFFM isthe same as the BFFM shown in FIG. 59 with the exception that the fourthfilter element 818 contains two layers of filter material of the sametype instead of four layers, and filter element 818′ has been addedin-between filter element 816 and filter element 817. Filter element 81′may be a first leukocyte removing filter element and may be made fromthe same type of filter material as filter element 818, in which casefilter element 818 would be a second leukocyte filter element. The firstBFFM can be used to filter blood or blood product as described in thefourteenth embodiment, with the additional benefit of having one largediameter leukocyte removing filter element 818′, thereby furtherreducing the leukocyte load on filter element 818. The second BFFMcontains three filter elements. When used to filter blood or bloodproduct filter element 1916 a could be a gel or microaggregate removingfilter element, filter element 1917 a could be a flow distributionfilter element, and filter element 1918 a could be a leukocyte removingfilter element. Alternatively filter element 1916 a could be a firstleukocyte removing filter element, filter element 1917 a could be a flowdistribution filter element, and filter element 1918 a could be a secondleukocyte removing filter element.

Any of the BFFM with the sealing methods shown in FIG. 37 of the eighthembodiment, or in FIG. 40, 41, 42, or 45, of the ninth embodiment, or inFIG. 46 of the tenth embodiment, or in FIG. 49 of the eleventhembodiment, or in FIG. 55 of the twelfth embodiment, or in FIG. 62 ofthe fifteenth embodiment, or in FIG. 75 of the sixteenth embodiment, orany combination thereof could also be used in place of the BFFM's shownin FIG. 94.

Referring to FIG. 94, FIG. 96, and FIG. 97, a first fluid flow path isdefined between first inlet 1905 of BFFD 1900 and first outlet 1927 ofBFFD 1900 with the first BFFM interposed between first inlet 1905 andfirst outlet 1927, and across the first fluid flow path. The first fluidflow path flows from first inlet 1905, through first cross port 1902,through first inlet slot 1988, into first upstream chamber first 1913,through the first BFFM, into first vertical channels 1922 a and 1922,into first arc outlet channel 1925, and then into first outlet 1927. Asecond fluid flow path is defined between second inlet 1905 a of BFFD1900 and second outlet 1927 a of BFFD 1900 with the second BFFMinterposed between second inlet 1905 a and second outlet 1927 a, andacross the second fluid flow path. The second fluid flow path flows fromsecond inlet 1905 a, through second cross port 1902 a, through secondinlet slot 1988 a, into second upstream chamber 1913 a, through thesecond BFFM, into second vertical channels 1922 b and 1922 c, intosecond arc outlet channel 1925 a, and then into second outlet 1927 a.The first fluid flow path is independent of the second fluid flow path,and there is no cross talk between the two. Solid partition wall 1937 isa barrier between the first fluid flow path and the second fluid flowpath.

Referring to FIG. 61 and FIG. 94, BFFD 1900 may replace BFFD 1500 inbiological fluid filtration system 3000. In this case the outlet end oftubing 83 is connected to first vent tube socket 1979 and the outlet endof tubing 83 a is connected to second vent tube socket 1979 a, theoutlet end of tubing 81 is connected to first inlet tube socket 1906,and the outlet end of tubing 81 b is connected to second inlet tubesocket 1906 a.

Referring to FIG. 61, and FIG. 93 through FIG. 97, the first fluid flowpath of BFFD 1900 functions as follows. When tube clamp 95 is openedbiological fluid will flow from feed blood bag 98, through tubing 81,through the first fluid flow path of BFFD 1900 by flowing into inlet1905, through first cross port 1902, through first inlet slot 1988, intofirst upstream chamber 1913, of BFFD 1900. First upstream chamber 1913will fill from the bottom up displacing the air that was in first theupstream chamber, and wetting the first BFFM as described above in thedescription of the fifteenth embodiment. Once the bottom of thedownstream surface of the first BFFM has become wetted, the downstreamsurface of the first BFFM will continue to wet from the bottom up, untilthe downstream surface of the first BFFM has become wetted to the levelof the top of the outermost first vertical channels 1922 a. At thispoint biological fluid will begin to flow into vertical channels 1922 afrom the bottom up, and then into arc outlet channel 1925, and then intooutlet 1927, and then into tubing 82. As the downstream surface of thefirst BFFM continues to wet vertically, biological fluid will begin toflow into successive vertical channels as the wetted level of thedownstream surface of the first BFFM reaches the top of each verticalchannel, and then flow into arc outlet channel 1925, and then intooutlet 1927, and then into tubing 82. If arc outlet channel 1925 issufficiently wide, a small quantity of biological fluid may enter arcoutlet channel 1925 before the wetted level of the downstream surface ofthe first BFFM reaches the top of vertical channels 1922 a. Hence theinitial flow of biological fluid into tubing 82 will consist ofalternate segments of liquid and air. However, all of the air will bepurged from within BFFD before the pressure downstream of the first BFFMand upstream of first outlet 1927 becomes negative.

Referring to FIG. 61 and FIG. 93 through FIG. 96, once all of the airhas been purged from within the first fluid flow path of BFFD 1900,biological fluid will continue to flow through the first fluid flow pathfrom the first inlet of BFFD 1900 to the first outlet of BFFD 1900, andthen through tubing 82 into first receiving blood bag 99 until firstfeed blood bag 98 is emptied of biological fluid. At this point firstfeed blood bag 98 will be collapsed, effectively sealing the top oftubing 81, thereby preventing the flow of biological fluid in tubing 81.With flow through tubing 81 shut off as just described, air will nowflow through a third fluid flow path from common vent port 1446 of ventfiltration device 1440, through the portion of vent filtration media1443 that is enclosed by the filter seal around the first filter supportstructure of vent filtration device 1440, through first system port 1444of vent filtration device 1440 through tubing 83, into first vent inlet1978, through first cross port 1902, through first inlet slot 1988, andthen into first upstream chamber 1913, thereby draining the biologicalfluid in first upstream chamber 1913 of BFFD 1900. To complete thedraining of biological fluid as just described, first receiving bloodbag 99 must be positioned a sufficient distance below first outlet 1927of BFFD 1900 to create a sufficiently negative pressure downstream ofthe first BFFM and upstream of first outlet 1927 after all of the airhas been purged from within BFFD 1900 and tubing 82 is filled withbiological fluid, to create a sufficient pressure differential betweenthe upstream surface and the downstream surface of the first BFFM todrain first upstream chamber 1913 to the bottom of first upstreamchamber 1913, because as the biological fluid level in first upstreamchamber 1913 approaches the bottom of first upstream chamber 1913, thepressure on the bottom of the biological fluid in first upstream 1913will approach zero.

Referring to FIG. 61, FIG. 93 and FIG. 94, when the filtration cyclethrough the first fluid flow path is complete as just described, thefirst BFFM will remain wetted, first vertical channels 1922 a and 1922,and first arc outlet channel 1925 will be filled with biological fluid,and tubing 82 will be filled with biological fluid. Because BFFD 1900does not contain a plenum downstream of the first BFFM, the hold upvolume of biological fluid within the first fluid flow path of BFFD 1900will be minimized.

The second fluid flow path of BFFD 1900 functions the same as the firstfluid flow path of BFFD 1900.

Once the filtration cycle through the first and second fluid flow pathsof BFFD 1900 is complete as just described, the user will close tubeclamp 96 and tube clamp 96 a, and then cut and seal tubing 82 above tubeclamp 96, and then cut and seal tubing 82 a above tube clamp 96 a, andthen discard BFFD 1900 and the remaining components attached to it in asafe manner.

The flow of biological fluid through first fluid flow path of BFFD 1900is completely independent of the flow of biological fluid through secondfluid flow path of BFFD 1900, because solid partition wall 1937 ofhousing outlet half 1920 isolates the first fluid flow path from thesecond fluid flow path.

Detailed Description of the Eighteenth Embodiment

A fourth embodiment of the biological fluid filtration system, and aneighteenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 80 through FIG.91. Biological fluid filtration system 4000 shown in FIG. 80 containsfeed blood 98, and receiving blood bag 99. Interposed between the feedblood bag and receiving blood bag is BFFD 1700. Three tube connector1650 is interposed between feed blood bag 98 and BFFD 1700. First lengthof tubing 81 connects the outlet of feed blood bag 98 to first tubesocket 1651 of three tube connector 1650. Second length of tubing 81 aconnects second tube socket 1652 of three tube connector 1650 to theinlet tube socket 1606 of BFFD 1700. Third length of tubing 1683connects third tube socket 1653 of three tube connector 1650 to tubesocket 1828 of diaphragm draining device 1800 (hereinafter referred toas DDD 1800). A fourth length of tubing 82 connects outlet tube socket1628 of BFFD 1700 to the inlet of receiving blood bag 99. A fifth lengthof tubing 84 connects a vent port on receiving blood bag 99 to tubesocket 1445 of vent filtration device 1440 a. A sixth length of tubing1684 connects outlet vent tube socket 1628 a to tube socket 1445 a ofvent filtration device 1440 a. Tubing 81 may contain tube clamp 95,tubing 82 may contain tube clamp 96, tubing 84 may contain tube clamp97, tubing 1683 may contain tube clamp 1694, and tubing 1684 mustcontain tube clamp 1697.

Referring to FIGS. 81 through 83, BFFD 1700 contains a rigid housingthat includes housing inlet half 101 b and housing outlet half 1620.Housing inlet half 101 b is the same as housing inlet half 101 shown inFIG. 16 except that housing inlet half 101 b does not contain a ventinlet, and flash trap 124″ does not contain a break for a hanging tab onthe housing outlet half. Housing outlet half 1620 is the same as housingoutlet half 120 shown in FIGS. 14 and 15, except that housing outlethalf 1620 does not contain a hanging tab, housing outlet half 1620 doescontain outlet vent 1627 a and outlet vent tube socket 1628 a, and thefilter under drain structure of housing outlet half 1620 does notcontain a circular outlet channel, instead it contains arc outletchannel 1625.

Referring to FIG. 81 and FIG. 82 housing outlet half 1620 containsfilter well 1611 bounded by inner side wall 1608 and by a plane thatgoes through filter seal surface 1624. Housing outlet half 1620 containsarc outlet channel 1625 and outlet 1627. Arc outlet channel 1625 is indirect fluid flow communication with outlet 1627, and the portion of arcoutlet channel 1625 that adjoins outlet 1627 has a cross-sectional flowarea that is greater than the cross-sectional flow area of outlet 1627.Arc outlet channel 1625 has an included angle substantially less than180° (i.e. substantially less than a semi-circle). Housing outlet half1620 also contains a plurality of open top closed bottom verticalchannels 1622 and 1622 a. The top end of each of the vertical channels1622 and 1622 a is in fluid flow communication with arc outlet channel1625. The vertical channels are shown non-tapered, but could be taperedin width and in depth. Arc outlet channel 1625 is sufficiently wide anddeep to accommodate the flow of biological fluid from vertical channels1622 and 1622 a. The two outermost vertical channels designated asvertical channels 1622 a adjoin arc outlet channel 1625 where the widthof arc outlet channel 1625 is equal to the width of the verticalchannels. The arc outlet channel and the vertical channels combined,create a filter under drain structure, and are cut into inner wall 1621of wall 1637, so that the inner surface of all of the channels liesbelow inner wall 1621, as shown in FIG. 82. The cross sectional area ofthe arc outlet channel and of the vertical channels is defined by theinner surface of each channel and by the downstream surface of the BFFM.As shown in FIG. 82, the distance between vertical channels 1622 and1622 a is much greater than the width of vertical channels 1622 and 1622a; and the distance between vertical channels 1622 and 1622 a is alsomuch greater than the depth of vertical channels 1622 and 1622 a.Because housing outlet half 1620 does not contain an open chamber orplenum downstream of the BFFM, hold up volume of biological fluid isminimized.

Referring to FIG. 81, BFFD 1700 contains a BFFM that is the same as thefirst BFFM shown in FIG. 62 of BFFD 1500 and described in the fifteenthembodiment above, except that filter element 1618 of the BFFM shown inFIG. 81 contains two layers of filter material of the same type.

Referring to FIG. 81, a first fluid flow path is defined between inlet105 of BFFD 1700 and outlet 1627 of BFFD 1700 with the BFFM interposedbetween inlet 105 and outlet 1627, and across the first fluid flow path.The first fluid flow path flows from inlet 105, through inlet slot 102,into upstream chamber 1613, through the BFFM, into vertical channels1622 and 1622 a, into arc outlet channel 1625, and then into outlet1627.

FIGS. 84 through 88 show diaphragm draining device 1800 (hereinafterreferred to as DDD 1800). DDD 1800 contains rigid housing inlet half1801, rigid housing outlet half 1820 and flexible diaphragm 1830. Rigidhousing inlet half contains inlet 1805, housing seal surface 1829,diaphragm counterbore 1850, and hanging tab 1831 that contains hanginghole 1830. Housing outlet half 1820 contains outlet 1827, outlet tubesocket 1828, and housing seal surface 1829 a. FIG. 84 shows DDD 1800 inits normal state with housing seal surface 1829 of housing inlet half1801 sealed to housing seal surface 1829 a of housing outlet half 1820.The seal is preferably an ultrasonic seal, but could be a heat seal, asolvent seal, a glue seal or any other type of leak tight seal. Flexiblediaphragm 1830 may be molded from a flexible rubber material such assilicone rubber, or it may be molded or thermo formed from a materialsuch as PVC, polyethylene, or polypropylene, but is not limited to thesematerials. Flexible diaphragm 1830 is preferably shaped so that in itsnormal state outer surface 1866 conforms to surface 1810 of housinginlet half 1801. Flexible diaphragm 1830 contains flange 1851 which maybe bonded to surface 1852 of housing inlet half 1801. The bond may be aheat bond, an ultrasonic bond, a glue bond, a solvent bond, or any othertype of leak tight bond. Alternately, flange 1851 may be compressionsealed between surface 1852 of housing inlet half 1801 and housing sealsurface 1829 a of housing outlet half 1820. FIG. 84 shows DDD 1800 inits normal state with outer surface 1866 in contact with surface 1810 ofhousing inlet half 1801. In its normal state, DDD 1800 contains chamber1813 that is in fluid flow communication with outlet 1827. In the normalstate chamber 1813 is filled with a gas (normally sterile air) atatmospheric pressure. FIG. 85 shows DDD 1800 with diaphragm 1830 in itscompletely collapsed state so that inner surface 1866 a of diaphragm1830 contacts inner surface 1810 a of housing outlet half 1820.

Referring to FIG. 89 three tube connector 1650 contains first tubesocket 1651, second tube socket 1652, and third tube socket 1653. Threetube connector also 1650 contains first channel 1654, second channel1655, and third channel 1656. Common node 1657 (shown as a dot) placeseach of the three channels in fluid flow communication with the othertwo channels. Second channel 1655 contains a flow restriction shown as achannel that is longer and smaller in diameter than the first and secondchannels. The first channel may be referred to as inlet 1654, the secondchannel may be referred to as outlet 1655, and the third channel may bereferred to as side port 1656. The shape of three tube connector 1650 isnot restricted to a tee as shown in FIG. 89, it could be in the form ofa Y, for example.

Vent filtration device 1440 a shown in FIG. 80 is the same as ventfiltration device 1440 shown in FIG. 73, except that housing cap 1441 a,shown in FIG. 90 and FIG. 91 is used in vent filtration device 1440 a.Housing cap 1441 a contains one or more vent ports 1446 a instead ofcommon vent port 1446 of housing cap 1441. Housing cap 1441 a alsocontains hanging tab 1460 that contains hanging hole 1461. Ventfiltration device 1440 a could be replaced with two separate ventfiltration devices.

Referring to FIG. 80, FIG. 84, and FIG. 89, a second fluid flow path isdefined between feed blood bag 98 and common node 1657 of three tubeconnector 1650, with the flow in the second fluid flow path flowing fromfeed blood bag 98 through tubing 81, into inlet 1654 of three tubeconnector 1650, to the common node. A third fluid flow path is definedbetween common node 1657 of three tube connector 1650 and inlet 105 ofBFFD 1700, with the flow in the third fluid flow path flowing fromcommon node 1657, through outlet 1655 (including the flow restriction),through tubing 81 a, to inlet 105 of BFFD 1700. A fourth fluid flow pathis defined between the common node and chamber 1813 of DDD 1800, withthe flow of the fourth fluid flow path flowing from chamber 1813,through outlet 1827 both of DDD 1800, through tubing 1683, through sideport 1656 of three tube connector 1650, to the common node of three tubeconnector 1650. Biological fluid filtration system 4000 contains tubing84 and vent filtration device 1440 a. One end of tubing 84 is connectedto tube socket 1445 of vent filtration device 1440 a and the other endof tubing 84 is connected to vent port 91 of receiving blood bag 99. Afifth fluid flow path is defined from atmosphere to vent port 91 ofreceiving blood bag 99. The fifth fluid flow path flows from vent port1446 a of vent filtration device 1440 a, through vent filtration media43 of vent filtration device 1440 a, through system port 1444 of ventfiltration device 1440 a through tubing 84, into vent port 91 ofreceiving blood bag 99, when tube clamp 97 is open. Preferably ventfiltration device 1440 a is located above the liquid level in feed bloodbag 98 as shown in FIG. 80. A sixth fluid flow path is defined fromatmosphere to outlet vent 1627 a of BFFD 1700. The sixth fluid flow pathflows from vent port 1446 a of vent filtration device 1440 a, throughvent filtration media 43 of vent filtration device 1440 a, throughsystem port 1444 a of vent filtration device 1440 a through tubing 1684,into outlet vent 1627 a of BFFD 1700 when tube clamp 1697 is open.

Referring to FIG. 80, FIG. 84, and FIG. 89, biological fluid filtrationsystem 4000 functions as follows. The user will purchase the system withall components as shown in FIG. 80, less feed blood bag 98. The userwill connect tubing 81 to outlet 92 of feed blood bag 98 in a mannerknown in the art. Feed blood bag 98, DDD 1800, and vent filtrationdevice 1440 a may be hung from hook 1747 of blood bag pole 1769, andreceiving blood bag 99 may be placed on a table top or the like, so thatthe various components of the system will be positioned as shown in FIG.80. However, it is not necessary to position DDD 1800 above the commonnode of three tube connector 1650, nor is it necessary to position ventfiltration device 1440 a above outlet vent 1627 a as long as tube clamps97 and 1697 are closed during the filtration cycle. Tube clamp 95 shouldbe closed before connecting tubing 81 to feed blood bag 98. Beforeopening tube clamp 95 to start the flow of biological fluid (i.e.liquid) through the system, tube clamps 1694 and 96 should be open, andtube clamp 97 and 1697 should be closed. When tube clamp 95 is openedbiological fluid (i.e. liquid) will flow from feed blood bag 98, throughtubing 81, into inlet 1654 of three tube connector 1650, through outlet1655 of three tube connector 1650, through tubing 81 a, into inlet 105of BFFD 1700, and then through inlet slot 102 of BFFD 1700, intoupstream chamber 1613 of BFFD 1700. Because outlet 1655 of three tubeconnector 1650 contains a flow restriction, the flow downstream of theinlet and downstream of the side port of the three tube connector willbe automatically restricted, and a positive pressure will be created atcommon node 1657 of three tube connector 1650. Also because flexiblediaphragm 1830 is sealed to DDD 1800 with a liquid/air tight seal, aircan not escape through inlet 1805 of DDD 1800. Therefore the air intubing 1683 and in chamber 1813 of DDD 1800 will be pressurized so thatonly a very small quantity of biological fluid if any will enter tubing1683. Upstream chamber 1613 will rapidly fill with biological fluid fromthe bottom up. As upstream chamber 1613 fills from the bottom up, theinitial air in upstream chamber 1613 will be displaced by the biologicalfluid filling upstream chamber 1613. The displaced air will be forcedthrough the BFFM, into vertical channels 1622 and 1622 a, into arcoutlet channel 1625, and then into outlet 1627 all of BFFD 1700. Thebiological fluid in upstream chamber 1613 will be pressurized, with thepressure at the bottom of upstream chamber 1613 being proportional tothe distance from the top of the biological fluid in feed blood bag 98to the bottom of upstream chamber 1613, and with the pressure at the topof upstream chamber 1613 being proportional to the distance from the topof the biological fluid in feed blood bag 98 to the top of upstreamchamber 1613. Hence the pressure at the top of upstream chamber 1613will be less than the pressure at the bottom of upstream chamber 1613.The positive pressure in upstream chamber 1613 will cause the biologicalfluid to flow through the BFFM over the entire surface area of the BFFMand to displace the air within the pores of the BFFM with biologicalfluid, thereby wetting BFFM from the upstream side of the BFFM to thedownstream side of the BFFM. As the BFFM wets the air that was initiallyin the pores of BFFM will be displaced by biological fluid and flow intovertical channels 1622 and 1622 e, and into arc outlet channel 1625, andthen into outlet 1627 all of BFFD 1700, into tubing 82, and then intoreceiving blood bag 99. Because the pressure at the bottom of upstreamchamber 1613 is greater than the pressure at the top of upstream chamber1613, the flow rate of biological fluid through the BFFM will be greaterat the bottom of the BFFM than at the top of the BFFM. Therefore, theBFFM will first become completely wetted from the upstream surface ofthe BFFM to downstream surface of the BFFM at the bottom of the BFFM. Ifthe width of vertical channels 1622 and 1622 a is sufficiently small,and the depth of vertical channels 1622 and 1622 a is sufficientlyshallow, so that the cross-sectional flow area of vertical channels 1622and 1622 a is sufficiently small, and if the distance between verticalchannels 1622 is sufficiently large, the path of least resistance forcontinued biological fluid flow through the BFFM will be through thecapillaries of the BFFM in both the horizontal and vertical directionsand not through the vertical channels, because if the cross-sectionalflow area of the vertical channels is sufficiently small, the displacedair flowing into and through the vertical channels will create asufficiently high positive pressure in the vertical channels to preventbiological fluid from entering the vertical channels. The downstreamsurface of the BFFM will therefore wet from the bottom up and thedisplaced air that was within the BFFM will continue to flow into thevertical channels, and into the arc outlet channel, and then into theoutlet. When the downstream surface of the BFFM has become wetted to thelevel of the top of vertical channels 1622 a, air flow through the twooutermost vertical channels 1622 a will stop because the downstreamsurface of the BFFM below the top of the two outermost vertical channelswill be wetted. Therefore the pressure in the two outermost verticalchannels will decrease allowing biological fluid to enter the twooutermost vertical channels from the bottom up, thereby displacing theair that was in the two outermost vertical channels. At the same timethe wetted level of the downstream surface of the BFFM will continue towet in the vertical direction, wetting the downstream surface of theBFFM adjoining arc outlet channel 1625. Because the cross-sectional flowarea of arc outlet channel 1625 is not sufficiently small to create apositive pressure in it due to the air flow through it, biological fluidwill begin to flow into vertical channels 1622 and into arc outletchannel 1625 as BFFM continues to wet in the vertical direction. Thebiological fluid flowing into vertical channels 1622 and 1622 a, andinto arc outlet channel 1625 will flow into outlet 1627 of BFFD 1700 andthen into tubing 82 toward receiving blood bag 99. As biological fluidstarts to flow into outlet 1627, the BFFM will continue to wetvertically. Hence the initial flow of biological fluid through arcoutlet channel 1625, and through outlet 1627, will be a mixture of airand biological fluid so that the initial flow into tubing 82 willconsist of alternate segments of biological fluid and air. As was beseen in the experimental data of the second embodiment, a BFFDconstructed in accordance with the principles of the present invention,as shown in FIG. 81 through FIG. 83, will purge approximately 98% of theinitial air in BFFD 1700 before biological fluid begins to flow intooutlet 1627.

Referring to FIG. 81 and FIG. 82, when biological fluid starts to flowinto tubing 82, the pressure P10 downstream of the BFFM and upstream ofoutlet 1627 (i.e. downstream of the BFFM, but within BFFD 1700) will bedetermined by the following formula:P10=L7−Δp−L8

-   -   Δp is the pressure drop across the BFFM due to biological fluid        flow through the BFFM.    -   L7 is the distance between outlet 1627 of BFFD 1700 and the top        of the biological fluid in feed blood bag 98.    -   L8 is the height of biological fluid minus any air segments        downstream of outlet 1627, in tubing 82.        Therefore the pressure P10 within BFFD 1700 and downstream of        the BFFM will be greater than or equal to zero until L8=L7−Δp.        Because the upper part of arc outlet channel 1625 is located a        sufficient distance above the horizontal center line of BFFD        1700, all of the air will be purged from within BFFD 1700 before        the pressure P10 becomes negative. As described above the        pressure within upstream chamber 1613 of BFFD 1700 will be        positive as long as biological fluid is flowing into upstream        chamber 1613. The purging of air from within BFFD 1700 is only        dependent upon the positive pressure upstream of the BFFM and is        totally independent of whether or not the pressure within BFFD        1700 downstream of the BFFM becomes negative.

Referring to FIG. 80, FIG. 81, FIG. 84 through FIG. 89, once all of theair has been purged from within BFFD 1700, biological fluid willcontinue to flow through the first fluid flow path from the inlet ofBFFD 1700 to the outlet of BFFD 1700, and then through tubing 82 intoreceiving blood bag 99 until feed blood bag 98 is emptied of biologicalfluid. At this point feed blood bag 98 will be collapsed, effectivelysealing the top of tubing 81, thereby preventing the flow of biologicalfluid in the second fluid flow path between the outlet of feed blood bag98 and common node 1657 of three tube connector 1650. If receiving bloodbag 99 is positioned a sufficient distance below BFFD 1700 to create asufficiently negative pressure downstream of the BFFM and upstream ofoutlet 1627 after all of the air has been purged from within BFFD 1700and tubing 82 is filled with biological fluid. The negative pressuredownstream of the BFFD will cause a suction force on the biologicalfluid in BFFD 1700 and in the biological fluid in tubing 81 a. Becausethe outer surface 1866 of flexible diaphragm 1830 is at atmosphericpressure via inlet 1805 of DDD 1800, the suction force willautomatically drain the biological fluid from tubing 1683, and from theside port 1656, and from outlet 1655 of DOD 1800, and from tubing 81 a,and from upstream chamber 1613, through the BFFM, through outlet 1627 ofBFFD 1700 through tubing 82, into receiving blood bag 99. The suctionforce will automatically cause flexible diaphragm 1830 to collapse sothat the air that was in chamber 1813 of DDD 1800 will displace thebiological fluid being drained from upstream of the BFFM. As long as thevolume of chamber 1813 of DOD 1800 is greater than or equal to thevolume of biological fluid being drained, all of the biological fluidwill be automatically drained as just described. FIG. 85 shows DDD 1800with diaphragm 1866 completely collapsed. If the volume of chamber 1813of DDD 1800 is greater than the volume of biological fluid beingdrained, then diaphragm 1866 will only partially collapse. When thefiltration cycle is complete, biological fluid will remain within theBFFM, and in the filter under drain structure of housing outlet half1620, and in tubing 82. DDD 1800 could replace vent filtration device 30shown in FIG. 1, or vent filtration device 40 shown in FIG. 12. Two DDD1800 could replace vent filtration device 1440 shown in FIG. 61. Theadvantage of replacing vent filtration devices with DDD's is that theDDD does not have a port that is open to atmosphere, therefore thesystem becomes a closed system.

Referring to FIG. 80, when the filtration cycle is complete as justdescribed, the user can open tube clamp 1697. If receiving blood bag 99is positioned a sufficient distance below outlet 1627 of BFFD 1700 sothat all of tubing 82 is positioned above receiving blood bag 99, airwill flow through the sixth fluid flow path from vent port 1446 a ofvent filtration device 1440 a, through vent filtration media 1443 ofvent filtration device 1440 a, through system port 1444 a of ventfiltration device 1440 a, through tubing 1684, into outlet vent 1627 aof BFFD 1700, and then into outlet 1627 of BFFD 1700, and then intotubing 82, thereby draining the biological fluid in tubing 82 intoreceiving blood bag 99. After mixing the biological fluid in receivingblood bag 99, a quantity of mixed biological fluid can be squeezed fromreceiving blood bag 99 back into tubing 82. Tube clamp 1697 may now beclosed thereby preventing the biological fluid that was just squeezedinto tubing 82 from draining. Tubing 82 may contain marks to divide itinto segments. In this case tubing 82 will now be sealed at each segmentso that the mixed biological fluid remaining in each segment could beused for cross matching and/or testing purposes. Tubing 82 can now becut above the top segment in tubing 82. Tube clamp 97 may now be opened,and the air in receiving blood bag 99 may be purged from receiving bloodbag 99 by squeezing receiving blood bag 99 thereby forcing the air inreceiving blood bag 99 through the fifth fluid flow path from vent port91 of receiving blood bag 99 to atmosphere. Tubing 84 can then be sealedand cut near receiving blood bag 99, and then tubing 84, vent filtrationdevice 1440 a, BFFD 1700 with all of the components attached to it maybe discarded in a safe manner. Alternately a quantity of biologicalfluid from receiving blood bag 99 may be squeezed into tubing 84 to beused for testing and/or cross matching purposes, after the air is purgedfrom the receiving blood bag. In this case tubing 84 may contain marksto divide it into segments. Tubing 84 would be sealed above the level ofbiological fluid in it, and at each segment mark, and then the portionof tubing 84 above the uppermost seal along with vent filtration device40 would be cut away and discarded in a safe manner.

Any of the BFFD's of previous embodiments could also contain an outletvent and an outlet vent tube socket, and be used in biological fluidfiltration system 4000.

Detailed Description of the Nineteenth Embodiment

A fifth embodiment of the biological fluid filtration system, and annineteenth embodiment of the BFFD constructed in accordance with theprinciples of the present invention, is shown in FIG. 92. Biologicalfluid filtration system 5000 shown in FIG. 92 contains feed blood 98,and receiving blood bag 99. Interposed between the feed blood bag andreceiving blood bag is BFFD 1700 a. BFFD 1700 a is the same as BFFD 1700shown in FIG. 81, except that BFFD 1700 a does not contain outlet vent1627 a and outlet vent tube socket 1628 a. Three tube connector 1650shown in FIG. 89 is interposed between feed blood bag 98 and BFFD 1700a. First length of tubing 81 connects outlet 92 of feed blood bag 98 tofirst tube socket 1651 of three tube connector 1650. Second length oftubing 81 a connects second tube socket 1652 of three tube connector1650 to the inlet tube socket 1606 of BFFD 1700 a. Third length oftubing 1683 connects third tube socket 1653 of three tube connector 1650to tube socket 45 of vent filtration device 40 a. Vent filtration device40 a is the same as vent filtration device 40 shown in FIG. 10, exceptthat housing cap 41 is replaced with a housing cap 1441 a shown in FIGS.90 and 91. Vent filtration device 40 a′ is the same as vent filtrationdevice 40 a. A fourth length of tubing 82 a connects outlet tube socket1628 of BFFD 1700 a to tube socket 51 of three tube connector 50 shownin FIG. 6. A fifth length of tubing 82 connects tube socket 52 of threetube connector 50 to receiving blood bag 99. A sixth length of tubing1684 a connects tube socket 53 of three tube connector 50 to tube socket45 of vent filtration device 40 a. A seventh length of tubing 1797connects the vent port of receiving blood bag 99 to the inlet port ofair bag 1799. Tubing 81 may contain tube clamp 95, tubing 82 may containtube clamp 96, tubing 82 a may contain tube clamp 96 a, tubing 1784 maycontain tube clamp 1797, tubing 1683 may contain tube clamp 1694, andtubing 1684 a must contain tube clamp 1697 a.

Referring to FIG. 89, and FIG. 92, biological fluid filtration system5000 functions as follows. The user will purchase the system with allcomponents as shown in FIG. 92, less feed blood bag 98. The user willconnect tubing 81 to outlet 92 of feed blood bag 98 in a manner known inthe art. Feed blood bag 98, and vent filtration devices 40 a may be hungfrom hook 1747 of blood bag pole 1769, with receiving blood bag 99 andair bag 1799 placed on a table top or the like, so that the variouscomponents of the system will be positioned as shown in FIG. 92.However, it is not necessary to position vent filtration device 40 a′above three tube connector 50 as long as tube clamp 1697 a is closedduring the filtration cycle. Tube clamp 95 should be closed beforeconnecting tubing 81 to feed blood bag 98. Before opening tube clamp 95to start the flow of biological fluid (i.e. liquid) through the system,tube clamps 1694, 96 and 96 a should be open, and tube clamp 1697 a and1797 should be closed. When tube clamp 95 is opened biological fluid(i.e. liquid) will flow from feed blood bag 98, through tubing 81, intoinlet 1654 of three tube connector 1650, through outlet 1655 of threetube connector 1650, through tubing 81 a, into inlet 105 of BFFD 1700 a,and then through inlet slot 102 of BFFD 1700 a, into upstream chamber1613 of BFFD 1700 a. Because outlet 1655 of three tube connector 1650contains a flow restriction the flow of biological fluid downstream ofthe inlet and of the side port of the three tube connector will beautomatically restricted, and a positive pressure will be created atcommon node 1657 of three tube connector 1650. The positive pressure atcommon node 1657 will force a quantity of biological fluid into tubing1683 with the displaced air in tubing 1683 being expelled through thevent ports 1446 a of vent filtration device 40 a. The positive pressureat common node 1657 will prevent air from entering tubing 81 a whilebiological fluid flows through tubing 81 and 81 a. Upstream chamber 1613will rapidly fill with biological fluid from the bottom up. BFFD 1700 awill wet, purge air, and filter the same as BFFD 1700 of the eighteenthembodiment. When feed blood bag 98 is emptied, it will be collapsed,effectively sealing the top of tubing 81, thereby preventing the flow ofbiological fluid in the fluid flow path between the outlet of feed bloodbag 98 and common node 1657 of three tube connector 1650. If receivingblood bag 99 is positioned a sufficient distance below BFFD 1700 a tocreate a sufficiently negative pressure downstream of the BFFM andupstream of outlet 1627 after all of the air has been purged from withinBFFD 1700 a and tubing 82 is filled with biological fluid, the negativepressure downstream of the BFFD will cause a suction force on thebiological fluid in BFFD 1700 a and in the biological fluid in tubing 81a. Because vent ports 1446 a of vent filtration device 40 a are open toatmosphere, the suction force will automatically drain the biologicalfluid from tubing 1683, the side port and outlet of three tube connector1650, from tubing 81 a, and from upstream chamber 1613 of BFFD 1700 a,with the drained biological fluid being displaced with air enteringtubing 1683 through vent filtration device 40 a.

Referring to FIG. 92, when the filtration cycle is complete as justdescribed, the user can close tube clamp 96 a and open tube clamp 1697a. If receiving blood bag 99 is positioned a sufficient distance belowoutlet 1627 of BFFD 1700 a so that all of tubing 82 is positioned abovereceiving blood bag 99, air will flow from vent ports 1446 a, throughvent filtration media 43, through system port 44 all of vent filtrationdevice 40 a′, through tubing 1684 a, through the side port and outlet ofthree tube connector 50, and then into tubing 82, thereby draining thebiological fluid from tubing 82 into receiving blood bag 99. Aftermixing the biological fluid in receiving blood bag 99, a quantity ofmixed biological fluid can be squeezed from receiving blood bag 99 backinto tubing 82. Tube clamp 1697 a may now be closed thereby preventingthe biological fluid that was just squeezed into tubing 82 fromdraining. Tubing 82 may contain marks to divide it into segments. Inthis case tubing 82 will now be sealed at each segment so that the mixedbiological fluid remaining in each segment could be used for crossmatching and/or testing purposes. Tubing 82 can now be cut above the topsegment in tubing 82 and BFFD 1700 a and the components attached to itcan be discarded in a safe manner. Tube clamp 1797 may now be opened,and the air in receiving blood bag 99 may be purged from receiving bloodbag 99 by squeezing receiving blood bag 99 thereby forcing the air inreceiving blood bag 99 through tubing 1784 into air bag 1799. Tubing1784 could then be sealed near receiving blood bag 99, and then cutabove the seal so that air bag 1799 could be discarded in a safe manner.Alternately a quantity of biological fluid from receiving blood bag 99may be squeezed into tubing 1784 to be used for testing and/or crossmatching purposes, after the air is purged from the receiving blood bag.In this case tubing 1784 may contain marks to divide it into segments.Tubing 1784 would be sealed above the level of biological fluid in it,and at each segment mark, and then the portion of tubing 84 above theuppermost seal along with air bag 1799 would be cut away and discardedin a safe manner. Vent filtration device 40 of FIG. 1 could be replacedwith air bag 1799 so that the air in receiving blood bag 99 of FIG. 1could be expressed into air bag 1799. Likewise, vent filtration device30 of FIG. 12 could be replaced with air bag 1799 so that the air inreceiving blood bag 99 of FIG. 12 could be expressed into air bag 1799.

1. A method of processing biological fluid comprising: a) providing abiological fluid filtration device having a first inlet, wherein thefirst inlet including an inlet end and an outlet end, and a first outletand at least one first filter element interposed between the first inletand the first outlet, and defining a first fluid flow path, that iscompletely independent of and isolated from a second fluid flow path,and that flows from the first inlet through the first filter elementinto the first outlet; said biological fluid filtration device furtherhaving a second inlet, wherein the second inlet includes an inlet endand an outlet end, wherein the outlet end of the second inlet iscompletely isolated from the outlet end of the first inlet within thedevice, and a second outlet and at least one second filter elementinterposed between the second inlet and the second outlet, and defininga second fluid flow path, that is completely independent of and isolatedfrom the first fluid flow path, and that flows from the second inletthrough the second filter element into the second outlet; saidbiological fluid filtration device further including a solid partitionwall interposed between the first fluid flow path and the second fluidflow path, with said solid partition wall isolating the entire firstfluid flow path, from the first inlet to the first outlet, from theentire second fluid flow path, from the second inlet to the secondoutlet; wherein, flow into said first outlet stops when flow into saidfirst inlet stops, and wherein, flow into said second outlet stops whenflow into said second inlet stops.
 2. A method of processing biologicalfluid comprising: a) providing a biological fluid filtration devicehaving a first inlet and a first outlet and at least one first filterelement interposed between the first inlet and the first outlet, anddefining a first fluid flow path, that is completely independent of andisolated from a second fluid flow path, and that flows from the firstinlet through the first filter element into the first outlet; saidbiological fluid filtration device further having a second inlet and asecond outlet and at least one second filter element interposed betweenthe second inlet and the second outlet, and defining a second fluid flowpath, that is completely independent of and isolated from the firstfluid flow path, and that flows from the second inlet through the secondfilter element into the second outlet; said biological fluid filtrationdevice further including a solid partition wall interposed between thefirst fluid flow path and the second fluid flow path, with said solidpartition wall isolating the entire first fluid flow path, from thefirst inlet to the first outlet, from the entire second fluid flow path,from the second inlet to the second outlet; wherein, flow into saidfirst inlet continues after flow into said first outlet starts, withflow into said first inlet stopping when the filtration of thebiological fluid through said first fluid flow path is complete; andwherein, flow into said second inlet continues after flow into saidsecond outlet starts, with flow into said second inlet stopping when thefiltration of the biological fluid through said second fluid flow pathis complete.
 3. A method of processing biological fluid comprising: a)providing a biological fluid filtration apparatus comprising: abiological fluid filtration device having a first inlet and a firstoutlet, and defining a first fluid flow path, that is completelyindependent of and isolated from a second fluid flow path, between thefirst inlet and the first outlet, and having at least one first filterelement interposed between the first inlet and the first outlet andacross the first fluid flow path, said biological fluid filtrationdevice further having a second inlet and a second outlet, and defining asecond fluid flow path, that is completely independent of and isolatedfrom the first fluid flow path, between the second inlet and the secondoutlet, and having at least one second filter element interposed betweenthe second inlet and the second outlet and across the second fluid flowpath, said biological fluid filtration device further including a solidpartition wall interposed between the entire first fluid flow path andthe entire second fluid flow path, with said solid partition wallisolating the entire first fluid flow path, from the first inlet to thefirst outlet, from the entire second fluid flow path, from the secondinlet to the second outlet, with said apparatus further including afirst collapsible blood bag with the interior of said first collapsibleblood bag in fluid flow communication with said first inlet, with saidapparatus also including a second collapsible blood bag with theinterior of said second collapsible blood bag in fluid flowcommunication with said first outlet and b) flowing biological fluidfrom said first collapsible blood bag, through said first inlet, throughsaid at least one first filter element, through said first outlet, intosaid second collapsible blood bag.
 4. The method of processingbiological fluid comprising: a) providing a biological fluid filtrationapparatus comprising: a biological fluid filtration device having afirst inlet and a first outlet, and defining a first fluid flow path,that is completely independent of and isolated from a second fluid flowpath, between the first inlet and the first outlet, and having at leastone first filter element interposed between the first inlet and thefirst outlet and across the first fluid flow path, said biological fluidfiltration device further having a second inlet and a second outlet, anddefining a second fluid flow path, that is completely independent of andisolated from the first fluid flow path, between the second inlet andthe second outlet, and having at least one second filter elementinterposed between the second inlet and the second outlet and across thesecond fluid flow path, said biological fluid filtration device furtherincluding a solid partition wall interposed between the entire firstfluid flow path and the entire second fluid flow path, with said solidpartition wall isolating the entire first fluid flow path, from thefirst inlet to the first outlet, from the entire second fluid flow path,from the second inlet to the second outlet, with said apparatus furtherincluding a first collapsible blood bag with the interior of said firstcollapsible blood bag in fluid flow communication with said first inlet,with said apparatus further including a second collapsible blood bagwith the interior of said second collapsible blood bag in fluid flowcommunication with said first outlet, with said apparatus furtherincluding a third collapsible blood bag with the interior of said thirdcollapsible blood bag in fluid flow communication with said secondinlet, with said apparatus further including a fourth collapsible bloodbag with the interior of said fourth collapsible blood bag in fluid flowcommunication with said second outlet, and b) flowing biological fluidfrom said first collapsible blood bag, through said first inlet, throughsaid at least one first filter element, through said first outlet, intosaid second collapsible blood bag, and c) flowing biological fluid fromsaid third collapsible blood bag, through said second inlet, throughsaid at least one second filter element, through said second outlet,into said fourth collapsible blood bag.
 5. The method of processingbiological fluid of claim 4 wherein said biological fluid is blood orblood product.
 6. The method of processing biological fluid of claim 5wherein said at least one first filter element is pore sized to removeleukocytes from the blood or blood product.
 7. The method of processingbiological fluid of claim 6 wherein said at least one first filterelement is used to filter blood or blood products, and wherein said atleast one first filter element includes: a) a first filter element poresized to remove gels from the blood or blood product, b) a second filterelement pore sized to remove microaggregates from the blood or bloodproduct, c) a third filter element pore sized to act as a flowdistribution layer, and d) a fourth filter element pore sized to removeleukocytes from the blood or blood product.
 8. The method of processingbiological fluid of claim 7 wherein said at least one second filterelement is used to filter blood or blood products, and wherein said atleast one second filter element includes: a) a first filter element poresized to remove microaggregates from the blood or blood product, b) asecond filter element pore sized to remove leukocytes from the blood orblood product, c) a third filter element pore sized to act as a flowdistribution layer, and d) a fourth filter element pore sized to removeparticulates from the blood or blood product.
 9. A method of processingbiological fluid comprising: a) providing a biological fluid filtrationdevice having a first inlet and a first outlet, and defining a firstfluid flow path, that is completely independent of, and isolated from, asecond fluid flow path, between the first inlet and the first outlet,and having at least one first filter element interposed between thefirst inlet and the first outlet and across the first fluid flow path,said biological fluid filtration device further having a second inletand a second outlet, and defining a second fluid flow path, that iscompletely independent of and isolated from the first fluid flow path,between the second inlet and the second outlet, and having at least onesecond filter element interposed between the second inlet and the secondoutlet and across the second fluid flow path, said biological fluidfiltration device further containing a solid partition wall interposedbetween the entire first fluid flow path and the entire second fluidflow path, with said solid partition wall isolating the entire firstfluid flow path, from the first inlet to the first outlet, from theentire second fluid flow path, from the second inlet to the secondoutlet, b) passing a first quantity of biological fluid through saidfirst fluid flow path, with the at least one first filter elementremoving the un-desired components of the first quantity of biologicalfluid from the first quantity of biological fluid, with the filteredfirst quantity of biological fluid containing the desired components ofthe first quantity of biological fluid flowing through said first outletand c) passing a second quantity of biological fluid through said secondfluid flow path, with the at least one second filter element removingthe un-desired components of the second quantity of biological fluidfrom the second quantity of biological fluid, with the filtered secondquantity of biological fluid containing the desired components of thesecond quantity of biological fluid flowing through said second outlet.10. A method of processing biological fluid comprising: providing abiological fluid filtration device having a first inlet and a firstoutlet, and defining a first fluid flow path between the first inlet andthe first outlet, and having at least one first filter elementinterposed between the first inlet and the first outlet and therebycausing a first quantity of biological fluid being filtered to flowthrough the at least one first filter element and out the first outlet,said biological fluid filtration device further having a second inletand a second outlet, and defining a second fluid flow path between thesecond inlet and the second outlet, and having at least one secondfilter element interposed between the second inlet and the second outletand thereby causing a second quantity of biological fluid being filteredto flow through the at least one second filter element and out thesecond outlet, with said biological fluid filtration device containing asolid partition wall interposed between the entire first fluid flow pathand the entire second fluid flow path, with said solid partition wallisolating the entire first fluid flow path, from the first inlet to thefirst outlet, from the entire second fluid flow path, from the secondinlet to the second outlet, wherein the filtered biological fluidflowing out of the first outlet does not contain any components of thebiological fluid flowing through the second fluid flow path, and whereinthe filtered biological fluid flowing out of the second outlet does notcontain any components of the biological fluid flowing through the firstfluid flow path.
 11. A method of processing biological fluid comprising:providing a biological fluid filtration device having a first inlet anda first outlet, and defining a first fluid flow path between the firstinlet and the first outlet, and having at least one first filter elementinterposed between the first inlet and the first outlet and therebycausing a first quantity of biological fluid being filtered to flowthrough the at least one first filter element and out the first outlet,said biological fluid filtration device further having a second inletand a second outlet, and defining a second fluid flow path between thesecond inlet and the second outlet, and having at least one secondfilter element interposed between the second inlet and the second outletand thereby causing a second quantity of biological fluid being filteredto flow through the at least one second filter element and out thesecond outlet, with said biological fluid filtration device containing asolid partition wall interposed between the entire first fluid flowpath, from the first inlet to the first outlet, and the entire secondfluid flow path, from the second inlet to the second outlet, wherein thefiltered biological fluid flowing out of the first outlet is completelyisolated from the filtered biological fluid flowing out of the secondoutlet by said solid partition wall.
 12. A method of processingbiological fluid comprising: providing a biological fluid filtrationdevice having a first inlet and a first outlet, and defining a firstfluid flow path between the first inlet and the first outlet, and havingat least one first filter element interposed between the first inlet andthe first outlet and thereby causing a first quantity of biologicalfluid being filtered to flow through the at least one first filterelement and out the first outlet, said biological fluid filtrationdevice further having a second inlet and a second outlet, and defining asecond fluid flow path between the second inlet and the second outlet,and having at least one second filter element interposed between thesecond inlet and the second outlet and thereby causing a second quantityof biological fluid being filtered to flow through the at least onesecond filter element and out the second outlet with said biologicalfluid filtration device containing a solid partition wall interposedbetween the entire first fluid flow path and the entire second fluidflow path, with said solid partition wall isolating the entire firstfluid flow path, from the first inlet to the first outlet, from theentire second fluid flow path, from the second inlet to the secondoutlet, thereby allowing a first type of biological fluid to be filteredthrough the first fluid flow path, and a second completely differenttype of biological fluid to be filtered through the second fluid flowpath.
 13. A method of processing biological fluid comprising: a)providing a biological fluid filtration device having a first inlet anda first outlet, and defining a first fluid flow path between the firstinlet and the first outlet, and having at least one first filter elementinterposed between the first inlet and the first outlet and therebycausing a first quantity of biological fluid, completely separate anddistinct from a second quantity of biological fluid, being filtered toflow through the at least one first filter element and out the firstoutlet, said biological fluid filtration device further having a secondinlet and a second outlet, and defining a second fluid flow path betweenthe second inlet and the second outlet, and having at least one secondfilter element interposed between the second inlet and the second outletand thereby causing a second quantity of biological fluid, completelyseparate and distinct from the first quantity of biological fluid, beingfiltered to flow through the at least one second filter element and outthe second outlet with said biological fluid filtration devicecontaining a solid partition wall interposed between the first fluidflow path and the second fluid flow path, with said solid partition wallisolating the entire first fluid flow path, from the first inlet to thefirst outlet, from the entire second fluid flow path, from the secondinlet to the second outlet, b) passing a first quantity of biologicalfluid through said first fluid flow path and c) passing a secondquantity of biological fluid through said second fluid flow path.
 14. Abiological fluid filtration device comprising: a) a housing containing afirst filter well on the first side of a solid partition wall, and asecond filter well on the second side of the solid partition wall, b) afirst biological fluid filtration media disposed in said first filterwell, and a second biological fluid filtration media disposed in saidsecond filter well, c) said housing also containing a first inlet and afirst outlet and defining a first fluid flow path between the firstinlet and the first outlet, thereby causing a first quantity ofbiological fluid, completely separate and distinct from a secondquantity of biological fluid, being filtered to flow through the firstbiological fluid filter media and out the first outlet, d) said housingfurther containing a second inlet and a second outlet, and defining asecond fluid flow path between the second inlet and the second outletthereby causing a second quantity of biological fluid, completelyseparate and distinct from the first quantity of biological fluid, beingfiltered to flow through the second biological fluid filter media andout the second outlet, e) with said first biological fluid filtrationmedia capable of removing un-desired components of biological fluid,while allowing the desired components of biological fluid to passthrough said first biological fluid filtration media, f) with saidsecond biological fluid filtration media capable of removing un-desiredcomponents of biological fluid, while allowing the desired components ofbiological fluid to pass through said second biological fluid filtrationmedia and g) with said solid partition wall completely isolating theentire first fluid flow path, from the first inlet to the first outlet,from the entire second fluid flow path, from the second inlet to thesecond outlet.
 15. A method of processing a biological fluid comprising:passing the biological fluid through a biological fluid filtrationdevice having a first inlet and a first outlet, and defining a firstfluid flow path between the first inlet and the first outlet, and havingat least one first filter element interposed between the first inlet andthe first outlet and across the first fluid flow path, said biologicalfluid filtration device further having a second inlet and a secondoutlet, and defining a second fluid flow path between the second inletand the second outlet, and having at least one second filter elementinterposed between the second inlet and the second outlet and across thesecond fluid flow path, said biological fluid filtration device furthercontaining a solid partition wall interposed between the first fluidflow path and the second fluid flow path, said solid partition wallcompletely isolating the entire first fluid flow path, from the firstinlet to the first outlet, from the entire second fluid flow path, fromthe second inlet to the second outlet, with the first filter elementlocated on one side of said solid partition wall, with the second filterelement located on the other side of said solid partition wall, therebyallowing a first type of biological fluid to be filtered through thefirst fluid flow path, and a second completely different type ofbiological fluid to be filtered through the second fluid flow path. 16.The method of processing the biological fluid of claim 15 wherein thefirst filter element is composed of a different type of filter materialthan the second filter element.
 17. The method of processing thebiological fluid of claim 15 wherein said first filter element includesan upstream side and a downstream side, and wherein said biologicalfluid filtration device further includes a vent port in fluid flowcommunication with the upstream side of said first filter element. 18.The method of processing a biological fluid of claim 17 wherein aventing means is connected to said vent port, with the venting meansallowing filtered air to enter said vent port after biological fluidfiltration through said first fluid flow path is complete, therebydraining the upstream side of said first filter element.
 19. A method ofprocessing a biological fluid comprising: passing the biological fluidthrough a biological fluid filtration device having a first inlet and afirst outlet, and defining a first fluid flow path between the firstinlet and the first outlet, and having at least one first filter elementinterposed between the first inlet and the first outlet and across thefirst fluid flow path, said biological fluid filtration device furtherhaving a second inlet and a second outlet, and defining a second fluidflow path between the second inlet and the second outlet, and having atleast one second filter element interposed between the second inlet andthe second outlet and across the second fluid flow path, said biologicalfluid filtration device further containing a solid partition wallinterposed between the first fluid flow path and the second fluid flowpath, said solid partition wall completely isolating the entire firstfluid flow path, from the first inlet to the first outlet, from theentire second fluid flow path, from the second inlet to the secondoutlet, with the first filter element located on one side of said solidpartition wall, with the second filter element located on the other sideof said solid partition wall, wherein the filtered biological fluidflowing out of the first outlet does not contain any components of thebiological fluid flowing through the second fluid flow path, and whereinthe filtered biological fluid flowing out of the second outlet does notcontain any components of the biological fluid flowing through the firstfluid flow path.
 20. A method of processing a biological fluidcomprising: passing the biological fluid through a biological fluidfiltration device having a first inlet and a first outlet, and defininga first fluid flow path between the first inlet and the first outlet,and having at least one first filter element interposed between thefirst inlet and the first outlet and across the first fluid flow path,said biological fluid filtration device further having a second inletand a second outlet, and defining a second fluid flow path between thesecond inlet and the second outlet, and having at least one secondfilter element interposed between the second inlet and the second outletand across the second fluid flow path, said biological fluid filtrationdevice further containing a solid partition wall interposed between thefirst fluid flow path and the second fluid flow path so that the entirefirst fluid flow path, from the first inlet to the first outlet, iscompletely isolated from the entire second fluid flow path, from thesecond inlet to the second outlet, by said solid partition wall, withthe first filter element disposed on one side of said solid partitionwall, with the second filter element disposed on the opposite side ofsaid solid partition wall, wherein the filtered biological fluid flowingout of the first outlet is completely isolated from the filteredbiological fluid flowing out of the second outlet by said solidpartition wall.
 21. A method of processing a biological fluidcomprising: a) providing a biological fluid filtration device having afirst inlet and a first outlet, and defining a first fluid flow pathbetween the first inlet and the first outlet, and having at least onefirst filter element interposed between the first inlet and the firstoutlet and across the first fluid flow path, said biological fluidfiltration device further having a second inlet and a second outlet, anddefining a second fluid flow path between the second inlet and thesecond outlet, and having at least one second filter element interposedbetween the second inlet and the second outlet and across the secondfluid flow path, said biological fluid filtration device furthercontaining a solid partition wall interposed between the first fluidflow path and the second fluid flow path, with said partition wallcompletely isolating the entire first fluid path, from the first inletto the first outlet, from the entire second fluid flow path, from thesecond inlet to the second outlet, with the at least one first filterelement disposed on one side of said solid partition wall, and with theat least one second filter element disposed on the other side of saidsolid partition wall, b) flowing a first quantity of biological fluidthrough said first fluid flow path, c) flowing a second quantity ofbiological fluid through said second fluid flow path.
 22. A method ofprocessing a biological fluid comprising: a) providing a biologicalfluid filtration device comprising: a self contained housing thatincludes a solid partition wall, with a first filter well on the firstside of said solid partition wall, and with a second filter well on thesecond side of said solid partition wall, a first filter elementincluding a first side and a second side, disposed inside of and sealedto said first filter well to prevent bypass around said first filterelement, a second filter element including a first side and a secondside, disposed inside of and sealed to said second filter well toprevent bypass around said second filter element, a first chamberlocated between the first side of said solid partition wall and thefirst side of said first filter element, a second chamber locatedbetween the second side of said first filter element and said housing, athird chamber located between the second side of said solid partitionwall and the first side of said second filter element, a fourth chamberlocated between the second side of said second filter element and saidhousing, a first port in fluid flow communication with said firstchamber, a second port in fluid flow communication with said secondchamber, a third port in fluid flow communication with said thirdchamber, a fourth port in fluid flow communication with said fourthchamber, a first fluid flow path flowing between said first and secondports, with said first fluid flow path flowing through said firstchamber, said first filter element and said second chamber, a secondfluid flow path flowing between said third and fourth ports, with saidsecond fluid flow path flowing through said third chamber, said secondfilter element and said fourth chamber, with the first and second fluidflow paths being completely independent of each other, and with saidsolid partition wall isolating the entire first fluid flow path, from afirst inlet to a first outlet, from the entire second fluid flow path,from a second inlet to a second outlet, b) flowing a first quantity ofbiological fluid through said first fluid flow path, thereby filteringsaid first quantity of biological fluid through said first filterelement; c) flowing a second quantity of biological fluid through saidsecond fluid flow path, thereby filtering said second quantity ofbiological fluid through said second filter element.
 23. A biologicalfluid filtration device comprising: a self contained housing thatincludes a solid partition wall, with a first filter well on the firstside of said solid partition wall, and with a second filter well on thesecond side of said solid partition wall; a first filter elementincluding a first side and a second side, disposed inside of and sealedto said first filter well to prevent bypass around said first filterelement; a second filter element including a first side and a secondside, disposed inside of and sealed to said second filter well toprevent bypass around said second filter element, a first chamberlocated between the first side of said solid partition wall and thefirst side of said first filter element, a second chamber locatedbetween the second side of said first filter element and said housing, athird chamber located between the second side of said solid partitionwall and the first side of said second filter element, a fourth chamberlocated between the second side of said second filter element and saidhousing, a first port in fluid flow communication with said firstchamber, a second port in fluid flow communication with said secondchamber, a third port in fluid flow communication with said thirdchamber; a fourth port in fluid flow communication with said fourthchamber, a first fluid flow path flowing between said first and secondports with said first fluid flow path flowing through said firstchamber, said first filter element and said second chamber; a secondfluid flow path flowing between said third and fourth ports, with saidsecond fluid flow path flowing through said third chamber, said secondfilter element and said fourth chamber, with said partition wallcompletely isolating the entire first fluid flow path, from a firstinlet to a first outlet, from the entire second fluid flow path, from asecond inlet to a second outlet.
 24. The biological fluid filtrationdevice of claim 23 wherein said housing further includes a vent port influid flow communication with said second chamber.